Methods and compositions for producing a chimeric polypeptide

ABSTRACT

The present invention provides methods and compositions for converting a first polypeptide into a chimeric polypeptide. The invention includes two vectors: a first vector including the sequence of the first polypeptide and a second vector including a second polypeptide. The vectors include complementary site-specific recombination motifs such that site-specific recombination between the two vectors results in the generation of a chimeric polypeptide including at least a portion of the first polypeptide and at least a portion of the second polypeptide. A site-specific recombination motif may be positioned within an intron or within a coding sequence on the first or second vector.

BACKGROUND OF THE INVENTION

Various methods have been utilized for the identification of bindingmoieties capable of binding particular antigens. Prior art methods havebeen used to generate antibodies or antibody fragments, such as IgG,IgM, IgA, IgD, IgE, Fab, Fab′, F(ab′)2, Fd, Fv, Feb, scFv, or SMIP.Because these types of binding moieties have distinct properties, it issometimes advantageous to convert a binding moiety of a first type intoa binding moiety of a second type. Certain existing methods for theconversion of a polypeptide of a first type to a polypeptide of a secondtype can be inefficient. Thus, there exists a need in the art forcompositions and methods for the efficient conversion of a polypeptideof a first type into a polypeptide of a second type (e.g., a chimericpolypeptide).

SUMMARY OF THE INVENTION

The present invention provides methods and compositions for converting apolypeptide of a first type into a chimeric polypeptide (e.g., apolypeptide of a different type) including at least a portion of thepolypeptide of the first type and, preferably, an additional polypeptideor a fragment thereof. In one embodiment, the invention includes twovectors: a first vector including the sequence of a first polypeptide(e.g., a binding moiety) and a second vector including the sequence of asecond polypeptide (e.g., a framework). It is appreciated that the terms“first vector” and “second vector,” and the terms “first polypeptide”and “second polypeptide,” may be interchangeable. The vectors mayfurther include complementary site-specific recombination motifs, suchthat site-specific recombination between the two vectors results in thegeneration of a chimeric polypeptide including at least a portion of thefirst polypeptide and at least a portion of the second polypeptide ofthe second vector.

In a first aspect, the invention features a method of converting asingle-chain variable fragment (scFv) into a chimeric polypeptide. Themethod involves:

(a) providing a first vector including, in order from 5′ to 3′,

-   -   a first mammalian expression control motif,    -   a first E. coli expression control motif,    -   a sequence encoding a heavy chain variable region (VH) of the        scFv,    -   a first site-specific recombination motif,    -   a sequence encoding a light chain variable region (VL) of the        scFv,    -   a 5′ mammalian splice site (Mam_(5′SS)),    -   a fusion display protein sequence,    -   a 3′ mammalian splice site (Mam_(3′SS)), and    -   a sequence encoding a light chain constant region (CL), and

(b) providing a second vector including, in order from 5′ to 3′,

-   -   a second mammalian expression control motif,    -   a second site-specific recombination motif, and    -   a sequence encoding a polypeptide; and

(c) contacting the first vector and the second vector in the presence ofa recombinase enzyme,

in which the recombinase enzyme combines the first vector and the secondvector in a site-specific manner to form an integrant vector,

in which the integrant vector expresses the VL fused to the CL and aseparate VH fused to the polypeptide,

thereby upon expression converting an scFv into a chimeric polypeptide.

In some embodiments of the first aspect, the first vector is a phagemidvector. In certain embodiments, the second vector is a phagemid vector.In one embodiment, the first vector is a phagemid vector and the secondvector is not a phagemid vector.

In some embodiments of the first aspect, the first vector furtherincludes: a 5′ mammalian splice site (Mam_(5′SS)) positioned between thefirst mammalian expression control motif and the first E. coliexpression control motif, and a 3′ mammalian splice site (Mam_(3′SS))positioned between the first E. coli expression control motif and thesequence encoding the VH of the scFv. In certain embodiments, the firstvector further includes a leader sequence positioned between the second3′ mammalian splice site and the sequence encoding the VH of the scFv.

In some embodiments of the first aspect, the first vector furtherincludes a leader sequence positioned between the first E. coliexpression control motif and the sequence encoding the VH of the scFv.

In some embodiments of the first aspect, the first vector furtherincludes: an additional 5′ mammalian splice site (Mam_(5′SS)) positionedbetween the sequence encoding the VH of the scFv and the firstsite-specific recombination motif, and an additional 3′ mammalian splicesite (Mam_(3′SS)) positioned between the first site-specificrecombination motif and the sequence encoding the VL of the scFv.

In some embodiments of the first aspect, the second vector furtherincludes: a further 5′ mammalian splice site (Mam_(5′SS)) positionedbetween the second mammalian expression control motif and the secondsite-specific recombination motif, and a further 3′ mammalian splicesite (Mam_(3′SS)) positioned between the second site-specificrecombination motif and the sequence encoding the polypeptide.

In some embodiments of the first aspect, the polypeptide includes aheavy chain constant region.

In some embodiments of the first aspect, the integrant vector expressesan IgG antibody.

In some embodiments of the first aspect, the polypeptide includes afusion protein. In certain embodiments, the fusion protein includes atag (e.g., a FLAG, HA, Myc, V5, His, GST, MBP, AviTag, streptavidin tag,or any other tag known in the art). In various embodiments, the fusionprotein includes a fluorescent protein (e.g., GFP, YFP, CFP, RFP, dsRed,mCherry, or any other fluorescent protein known in the art).

In some embodiments of the first aspect, the providing step furtherincludes providing an additional vector including a polynucleotideencoding the recombinase enzyme. In certain embodiments, the recombinaseenzyme is expressed by the additional vector.

In a second aspect, the invention features a method of converting afirst polypeptide into a chimeric polypeptide. The method involves:

-   -   (a) providing:        -   i. a first vector including a first polynucleotide encoding            a first polypeptide, the first polynucleotide including a            first site-specific recombination motif;        -   ii. a second vector including a second site-specific            recombination motif and a second polynucleotide encoding a            second polypeptide; and        -   iii. a recombinase enzyme capable of recombining the first            site-specific recombination motif with the second            site-specific recombination motif; and    -   (b) recombining the first vector and the second vector with the        recombinase enzyme, thereby forming a recombinant vector        encoding a chimeric polypeptide including:        -   i. the first polypeptide, or a portion thereof, and        -   ii. the second polypeptide, or a portion thereof.

In some embodiments of the second aspect, the first polypeptide-encodingregion of the first polynucleotide includes the first site-specificrecombination motif. In some embodiments, the first polypeptide includesa linker, and the portion of the polynucleotide encoding the linkerincludes the first site-specific recombination motif. In certainembodiments, the first vector or the second vector includes apolynucleotide encoding the recombinase enzyme. In particularembodiments, the providing step further includes providing an additionalvector including a polynucleotide encoding the recombinase enzyme.

In a third aspect, the invention features a method of converting a firstpolypeptide into a chimeric polypeptide. The method involves:

-   -   (a) providing:        -   i. a first vector including a first polynucleotide encoding            a first polypeptide, the first polynucleotide including an            intron including a first site-specific recombination motif;        -   ii. a second vector including a second site-specific            recombination motif and a second polynucleotide encoding a            second polypeptide; and        -   iii. a recombinase enzyme capable of recombining the first            site-specific recombination motif with the second            site-specific recombination motif; and    -   (b) recombining the first vector and the second vector with the        recombinase enzyme, thereby forming a recombinant vector        encoding a chimeric polypeptide including:        -   i. the first polypeptide, or a portion thereof, and        -   ii. the second polypeptide, or a portion thereof.

In some embodiments of the third aspect, the portion of the firstpolynucleotide encoding the first polypeptide includes the intron. Incertain embodiments, the portion of the first polynucleotide encodingthe first polypeptide does not include the intron. In particularembodiments, the first vector or the second vector includes apolynucleotide encoding the recombinase enzyme.

In some embodiments of the third aspect, the providing step furtherincludes providing an additional vector including a polynucleotideencoding the recombinase enzyme.

In a fourth aspect, the invention features a method of converting afirst polypeptide into one of at least two chimeric polypeptides. Themethod involves:

(a) providing a first vector including a first polynucleotide encoding afirst polypeptide including a first site-specific recombination motifand an alternate site-specific recombination motif, and

-   -   i. a second vector including a second site-specific        recombination motif and a second polynucleotide encoding a        second polypeptide; and a recombinase enzyme capable of        recombining the first site-specific recombination motif with the        second site-specific recombination motif; or    -   ii. a third vector including a third site-specific recombination        motif distinct from the first site-specific recombination motif        and an alternate polynucleotide encoding an alternate        polypeptide; and an alternate recombinase enzyme capable of        recombining the alternate site-specific recombination motif with        the third site-specific recombination motif; and

(b) recombining the first vector and:

-   -   i. the second vector with the recombinase enzyme, thereby        forming a recombinant vector encoding a chimeric polypeptide        including the first polypeptide, or a portion thereof, and the        second polypeptide, or a portion thereof; and/or    -   ii. the third vector with the alternate recombinase enzyme,        thereby forming a recombinant vector encoding a chimeric        polypeptide including the first polypeptide, or a portion        thereof, and the alternate polypeptide, or a portion thereof.

In some embodiments of the fourth aspect, the first polynucleotideincludes the first site-specific recombination motif. In certainembodiments, the first polynucleotide includes an intron including thefirst site-specific recombination motif. In various embodiments, thesecond polynucleotide includes an intron including the secondsite-specific recombination motif. In particular embodiments, the firstvector or the second vector includes a polynucleotide encoding therecombinase enzyme, and/or the first vector or the third vector includesa polynucleotide encoding the alternate recombinase enzyme.

In a fifth aspect, the invention features a method of converting an scFvinto a chimeric polypeptide. The method involves:

-   -   (a) providing:        -   i. a first vector including a first polynucleotide encoding            a first polypeptide including an scFv including a light            chain variable domain, a linker region, and a heavy chain            variable domain, the portion of the first polynucleotide            encoding the linker region including a first site-specific            recombination motif (e.g., an attP site);        -   ii. a second vector including a second site-specific            recombination motif and a second polynucleotide encoding a            second polypeptide; and        -   iii. a recombinase enzyme capable of recombining the first            site-specific recombination motif with the second            site-specific recombination motif; and    -   (b) recombining the first vector and the second vector with the        recombinase enzyme, thereby forming a recombinant vector        encoding a chimeric polypeptide including:        -   i. the light chain variable domain and/or the heavy chain            variable domain, and        -   ii. the second polypeptide, or a portion thereof;

in which the chimeric polypeptide is not an scFv.

In some embodiments of any of the first through fifth aspects, the firstpolypeptide includes an antibody or antibody fragment. In certainembodiments, the antibody or antibody fragment is a human, mouse, goat,sheep, rabbit, chicken, guinea pig, hamster, horse, or rat antibody orantibody fragment. In various embodiments, the antibody is an IgG, IgA,IgD, IgE, IgM, or intrabody. In one embodiment, the antibody is an IgG.

In certain embodiments, the antibody fragment includes an scFv,single-domain antibody (sdAb), dAb, Fab, Fab′, Fab′2, F(ab′)2, Fd, Fv,Feb, or SMIP. In particular embodiments, the antibody fragment is anscFv. In one embodiment, the scFv is a cytosol-stable scFv. In certainembodiments, the scFv is a bovine scFv. In one embodiment, the sdAb is acamelid VHH. In various embodiments, the scFv includes a linkerpositioned between the light chain variable domain and the heavy chainvariable domain of the scFv, the linker including the firstsite-specific recombination motif. In specific embodiments, the chimericpolypeptide includes the light chain variable domain of the scFv and/orthe heavy chain variable domain of the scFv.

In some embodiments of any of the first through fifth aspects, the firstpolypeptide includes a chimeric antigen receptor (CAR). In certainembodiments, the first polypeptide includes a CD8 transmembrane domain,CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmic domain, and/or CD28cytoplasmic domain. In certain embodiments, the chimeric polypeptideincludes the CD8 transmembrane domain, CD3-zeta cytoplasmic domain, 4-1BB cytoplasmic domain, and/or CD28 cytoplasmic domain of the firstpolypeptide. In various embodiments, the chimeric polypeptide furtherincludes a peptide linker domain positioned between: (i) the CD8transmembrane domain, CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmicdomain, and/or CD28 cytoplasmic domain of the first polypeptide, and(ii) the first polypeptide, or the portion thereof. In particularembodiments, the peptide linker domain has a length of about 0-250 aminoacids or about 1-250 amino acids (e.g., about 1-50, 1-10, 10-20, 20-50,or 50-100 amino acids). In a preferred embodiment, the peptide linkerdomain has a length of about 1-50 amino acids. In certain embodiments,the CAR includes an extracellular binding moiety (e.g., an scFv) capableof binding to an antigen associated with a disease. In particularembodiments, the disease is a cell proliferation disorder, such ascancer. In specific embodiments, the antigen is a tumor-associatedantigen. In one embodiment, the antigen is CD19 and the disease is acutelymphoblastic leukemia (ALL).

In various embodiments, the chimeric polypeptide includes an antibody orantibody fragment. In particular embodiments, the antibody or antibodyfragment is a human, mouse, goat, sheep, rabbit, chicken, guinea pig,hamster, horse, or rat antibody or antibody fragment. In specificembodiments, the antibody is an IgG, IgA, IgD, IgE, IgM, or intrabody.In various embodiments, the antibody is an IgG. In particularembodiments, the first polypeptide includes the variable light chainand/or variable heavy chains of the IgG. In specific embodiments, thefirst vector includes a polynucleotide encoding a constant domain of theIgG. In a particular embodiment, the constant domain includes a CLdomain or an Fc domain. In one embodiment, the constant domain includesa CH domain including the Fc domain.

In certain embodiments, the antibody fragment includes an scFv, sdAb,dAb, Fab, Fab′, Fab′2, F(ab′)2, Fd, Fv, Feb, or SMIP. In particularembodiments, the antibody fragment is an scFv. In specific embodiments,the scFv is a cytosol-stable scFv. In an embodiment, the scFv is abovine scFv. In one embodiment, the sdAb is a camelid VHH.

In some embodiments of any of the first through fifth aspects, thechimeric polypeptide includes a chimeric antigen receptor (CAR). Incertain embodiments, the second polypeptide includes a CD8 transmembranedomain, CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmic domain, and/orCD28 cytoplasmic domain. In particular embodiments, the firstpolypeptide is an scFv and the chimeric polypeptide includes the lightchain variable domain of the scFv and the CD8 transmembrane domain,CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmic domain, and/or CD28cytoplasmic domain. In various embodiments, the chimeric polypeptidefurther includes a peptide linker domain positioned between: (i) thelight chain variable domain of the scFv, and (ii) the CD8 transmembranedomain, CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmic domain, and/orCD28 cytoplasmic domain. In particular embodiments, the peptide linkerdomain has a length of about 0-250 amino acids or about 1-250 aminoacids (e.g., about 1-50, 1-10, 10-20, 20-50, or 50-100 amino acids). Ina preferred embodiment, the peptide linker domain has a length of about1-50 amino acids. In specific embodiments, the first polypeptide is anscFv and the chimeric polypeptide includes the heavy chain variabledomain of the scFv and the CD8 transmembrane domain, CD3-zetacytoplasmic domain, 4-1 BB cytoplasmic domain, and/or CD28 cytoplasmicdomain. In various embodiments, the chimeric polypeptide furtherincludes a peptide linker domain positioned between: (i) the heavy chainvariable domain of the scFv, and (ii) the CD8 transmembrane domain,CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmic domain, and/or CD28cytoplasmic domain. In particular embodiments, the peptide linker domainhas a length of about 0-250 amino acids or about 1-250 amino acids(e.g., about 1-50, 1-10, 10-20, 20-50, or 50-100 amino acids). In apreferred embodiment, the peptide linker domain has a length of about1-50 amino acids. In other embodiments, the first polypeptide is an scFvand the chimeric polypeptide includes the heavy chain variable domainand the light chain variable domain of the scFv and the CD8transmembrane domain, CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmicdomain, and/or CD28 cytoplasmic domain. In various embodiments, thechimeric polypeptide further includes a peptide linker domain positionedbetween: (i) the heavy chain variable domain and the light chainvariable domain of the scFv, and (ii) the CD8 transmembrane domain,CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmic domain, and/or CD28cytoplasmic domain. In particular embodiments, the peptide linker domainhas a length of about 0-250 amino acids or about 1-250 amino acids(e.g., about 1-50, 1-10, 10-20, 20-50, or 50-100 amino acids). In apreferred embodiment, the peptide linker domain has a length of about1-50 amino acids. In certain embodiments, the CAR includes anextracellular binding moiety (e.g., an scFv) capable of binding to anantigen associated with a disease. In particular embodiments, thedisease is a cell proliferation disorder, such as cancer. In specificembodiments, the antigen is a tumor-associated antigen. In oneembodiment, the antigen is CD19 and the disease is acute lymphoblasticleukemia (ALL).

In some embodiments of any of the first through fifth aspects, thechimeric polypeptide includes an ubiquitin ligase domain. In certainembodiments, the second polypeptide includes the ubiquitin ligasedomain. In particular embodiments, the ubiquitin ligase domain includesa CHIPΔTPR domain.

In some embodiments of any of the first through fifth aspects, thechimeric polypeptide includes a knocksideways prey domain. In certainembodiments, the second polypeptide includes the knocksideways preydomain. In specific embodiments, the knocksideways prey domain includesan FKBP domain. In certain embodiments, the providing step furtherincludes providing a knocksideways bait protein. In particularembodiments, the knocksideways bait protein includes an FRB domain. Inspecific embodiments, the knocksideways bait protein includes amitochondrial outer membrane targeting signal. In one embodiment, theknocksideways bait protein is a Mitotrap protein.

In certain embodiments, the chimeric polypeptide further includes aubiquitin ligase domain. In particular embodiments, the secondpolypeptide includes the ubiquitin ligase domain. In one embodiment, theubiquitin ligase domain includes a CHIPΔTPR domain.

In some embodiments of any of the first through fifth aspects, therecombinase enzyme is a serine family recombinase or a tyrosine familyrecombinase. In certain embodiments, the serine family recombinase isphiC31, BxB1, HIN invertase, or TN3 resolvase. In one embodiment, theserine family recombinase is phiC31. In certain embodiments, theproviding step further includes providing an accessory factor. In oneembodiment, the accessory factor includes Xis. In certain embodiments,the tyrosine family recombinase is bacteriophage lambda integrase, Cre,or Flp. In particular embodiments, the recombinase is selected from theintegrases shown in Table 2.

In some embodiments of any of the first through fifth aspects, the firstpolypeptide, the second polypeptide, and/or the chimeric polypeptideincludes a marker. In certain embodiments, the marker is an epitope tagand/or a fluorescent protein. In particular embodiments, the epitope tagis a FLAG, HA, Myc, V5, His, GST, MBP, AviTag, or streptavidin tag, orany other epitope tag known in the art. In particular embodiments, thefluorescent protein is EGFP, GFP, YFP, CFP, mCherry, dsRed, or any otherfluorescent protein known in the art.

In some embodiments of any of the first through fifth aspects, therecombining step takes place in a cell. In particular embodiments, thecell is included in an emulsion droplet. In certain embodiments, theproviding step further includes providing the cell, and the cellincludes the vectors and the recombinase enzyme. In certain embodiments,the first vector is a plasmid or a phagemid. In particular embodiments,the first vector includes a polynucleotide encoding a display protein.In specific embodiments, the display protein is capable of displayingthe first polypeptide, or a portion thereof, on the extracellularsurface of a cell (e.g., the cell in which the recombining step takesplace). In one embodiment, the display protein includes ompA. In anotherembodiment, the display protein includes bclA. In various embodiments,the cell is a bacterial cell. In particular embodiments, the bacterialcell is E. coli. In various embodiments, the cell is a eukaryotic cell.In particular embodiments, the eukaryotic cell is a mammalian cell or aninsect cell.

In certain embodiments, the cell further includes a vector including apolynucleotide encoding the recombinase enzyme. In one embodiment, thecell further includes a chromosome including a polynucleotide encodingthe recombinase enzyme.

In some embodiments of any of the first through fifth aspects, therecombining step takes place in a cell-free system. In certainembodiments, the cell-free system is a solution including the vectorsand the recombinase enzyme. In one embodiment, the recombinase enzyme isbacteriophage lambda integrase. In various embodiments, the cell freesystem is included in an emulsion droplet. In particular embodiments, aplurality of such recombining steps can occur in a plurality of emulsiondroplets in parallel. Massively multiplex recombination reactions inparallel, e.g., in such emulsion droplets, is contemplated. Suchmultiplex systems may include, for example, any liquid handling oremulsion droplet-based system known in the art.

In some embodiments of any of the first through fifth aspects, the firstvector includes a plurality of distinct regulatory elements positionedadjacent to each other. In certain embodiments, one of the regulatoryelements controls the expression of the first polypeptide, or a portionthereof, in a first cell type, and another of the regulatory elementscontrols the expression of the first polypeptide, or a portion thereof,in a second cell type. In particular embodiments, the first polypeptide,or portion thereof is fused to a protein fragment when expressed in thefirst cell type. In specific embodiments, the protein fragment includesa viral coat protein. In one embodiment, the viral coat protein is M13gpIII. In certain embodiments, the protein fragment further includes abacterial signal peptide. In certain embodiments, the first cell type isa bacterial cell, and the second cell type is a eukaryotic cell. In oneembodiment, the bacterial cell is an E. coli cell. In particularembodiments, the eukaryotic cell is a mammalian cell, insect cell, orfungal cell. In one embodiment, the mammalian cell is a human cell. Inanother embodiment, the fungal cell is a yeast cell.

In some embodiments of any of the first through fifth aspects, thesecond vector includes a plurality of distinct regulatory elementspositioned adjacent to each other. In certain embodiments, one of theregulatory elements controls the expression of the second polypeptide,or a portion thereof, in a first cell type, and another of theregulatory elements controls the expression of the second polypeptide,or a portion thereof, in a second cell type. In particular embodiments,the second polypeptide, or portion thereof is fused to a proteinfragment when expressed in the first cell type. In specific embodiments,the protein fragment includes a viral coat protein. In one embodiment,the viral coat protein is M13 gpIII. In certain embodiments, the proteinfragment further includes a bacterial signal peptide. In certainembodiments, the first cell type is a bacterial cell, and the secondcell type is a eukaryotic cell. In one embodiment, the bacterial cell isan E. coli cell. In particular embodiments, the eukaryotic cell is amammalian cell, insect cell, or fungal cell. In one embodiment, themammalian cell is a human cell. In another embodiment, the fungal cellis a yeast cell.

In some embodiments of any of the first through fifth aspects, therecombinant vector includes a plurality of distinct regulatory elementspositioned adjacent to each other. In various embodiments, one of theregulatory elements controls the expression of the chimeric polypeptidein a first cell type, and another of the regulatory elements controlsthe expression of the chimeric polypeptide in a second cell type. Incertain embodiments, the first cell type is a bacterial cell, and thesecond cell type is a eukaryotic cell. In one embodiment, the bacterialcell is an E. coli cell. In particular embodiments, the eukaryotic cellis a mammalian cell, insect cell, or fungal cell. In one embodiment, themammalian cell is a human cell. In another embodiment, the fungal cellis a yeast cell.

In certain embodiments of any of the above, one or more of the distinctregulatory elements is a promoter. In particular embodiments, thepromoter is a bacterial promoter (e.g., a lac promoter, T7 promoter, orT3 promoter). In one embodiment, the bacterial promoter is a lacpromoter. In other embodiments, the promoter is a eukaryotic promoter(e.g., a promoter capable of controlling expression in a mammalian cell,an insect cell, or a fungal cell). In one embodiment, the promotercapable of controlling expression in a mammalian cell is a CMV promoteror an EF1a promoter. In another embodiment, the promoter capable ofcontrolling expression in an insect cell is a polyhedron promoter.

In some embodiments of any of the first through fifth aspects, the firstpolynucleotide includes an intron including an intronic regulatoryelement. In certain embodiments, the intronic regulatory elementcontrols the expression of the first polypeptide, or a portion thereof,in a prokaryotic cell. In particular embodiments, the prokaryotic cellis a bacterial cell. In one embodiment, the bacterial cell is E. coli.In various embodiments, the first polypeptide, or portion thereof, isfused to a protein fragment when expressed in the prokaryotic cell. Incertain embodiments, the protein fragment includes a viral coat protein.In one embodiment, the viral coat protein is M13 gpIII. In variousembodiments, the protein fragment further includes a bacterial signalpeptide. In certain embodiments, the intron further includes apolynucleotide encoding the protein fragment. In particular embodiments,the intronic regulatory element controls the expression of the proteinfragment. In one embodiment, the intronic regulatory element is removedfrom the transcript of the first polynucleotide in a eukaryotic cell byRNA splicing. In certain embodiments, the eukaryotic cell is a mammaliancell, insect cell, or fungal cell.

In certain embodiments, the intronic regulatory element is a promoter.In particular embodiments, the promoter is a bacterial promoter (e.g., alac promoter, T7 promoter, or T3 promoter). In one embodiment, thebacterial promoter is a lac promoter. In other embodiments, the promoteris a eukaryotic promoter (e.g., a promoter capable of controllingexpression in a mammalian cell, an insect cell, or a fungal cell). Inone embodiment, the promoter capable of controlling expression in amammalian cell is a CMV promoter or an EF1a promoter. In anotherembodiment, the promoter capable of controlling expression in an insectcell is a polyhedron promoter.

In some embodiments of any of the first through fifth aspects, the firstvector further includes a pair of complementary site-specificrecombination motifs (e.g., two loxP sites, two FRT sites, or an attBsite and an attP site). In certain embodiments, the firstpolynucleotide, a fragment thereof, and/or the first site-specificrecombination motif are located between the pair of complementarysite-specific recombination motifs. In some embodiments of any of thefirst through fifth aspects, the second vector further includes a pairof complementary site-specific recombination motifs. In certainembodiments, the second polynucleotide, a fragment thereof, and/or thesecond site-specific recombination motif are located between the pair ofcomplementary site-specific recombination motifs.

In certain embodiments, the pair of complementary site-specificrecombination motifs are oriented such that recombination of the pair ofcomplementary site-specific recombination motifs results in theinversion of the intervening sequences. In other embodiments, the pairof complementary site-specific recombination motifs are oriented suchthat recombination of the pair of complementary site-specificrecombination motifs results in the deletion of the interveningsequences.

In certain embodiments, the providing step further includes providing arecombinase enzyme capable of recombining the pair of complementarysite-specific recombination motifs (e.g., Cre, FRT, phiC31, orbacteriophage lambda integrase). In particular embodiments, the methodfurther includes the step of recombining the pair of complementarysite-specific recombination motifs. In specific embodiments, the pair ofcomplementary site-specific recombination motifs includes a pair of loxPsites. In one embodiment, the providing step further includes providinga Cre recombinase enzyme. In specific embodiments, the pair ofcomplementary site-specific recombination motifs includes a pair of FRTsites. In one embodiment, the providing step further includes providinga Flp recombinase enzyme. In specific embodiments, the pair ofcomplementary site-specific recombination motifs includes an attB siteand an attP site. In certain embodiments, the providing step furtherincludes providing a recombinase enzyme (e.g., phiC31 or BxB1) capableof recombining said first site-specific recombination motif and/or saidsecond site-specific recombination motif, and a distinct recombinaseenzyme (e.g., BxB1, phiC31, Cre, or Flp) capable of recombining the pairof complementary site-specific recombination motifs. In one embodiment,the providing step further includes providing a phiC31 or BxB1recombinase enzyme suitable for recombining the attB site and the attPsite of the pair of complementary site-specific recombination motifs.

In some embodiments of any of the first through fifth aspects, the firstvector is a viral vector. In certain embodiments, the first vector is anadenoviral, lentiviral, or baculoviral vector. In some embodiments ofany of the first through fifth aspects, the second vector is a viralvector. In certain embodiments, the second vector is an adenoviral,lentiviral, or baculoviral vector. In certain embodiments, one or moreviral elements are located within an intron.

In some embodiments of any of the first through fifth aspects, the firstvector is a phagemid vector. In some embodiments of any of the firstthrough fifth aspects, the second vector is a phagemid vector.

In some embodiments of any of the first through fifth aspects, the firstvector further includes a first recombination motif fragment and thesecond vector includes a second recombination motif fragment, and therecombinant vector includes a cryptic site-specific recombination motifincluding the first recombination motif fragment and the secondrecombination motif fragment, and

the method further includes:

(c) recombining the recombinant vector and a further vector including

-   -   (i) a further site-specific recombination motif, and    -   (ii) a polynucleotide encoding a further polypeptide;

with a further recombinase enzyme capable of recombining the crypticsite-specific recombination motif with the further site-specificrecombination motif,

thereby forming a second recombinant vector encoding a second chimericpolypeptide including:

-   -   (i) the chimeric polypeptide, or a portion thereof, and    -   (ii) the further polypeptide, or a portion thereof.

In certain embodiments, the first site-specific recombination motif andthe cryptic site-specific recombination motif are the same. In otherembodiments, the first site-specific recombination motif and the crypticsite-specific recombination motif are different. In various embodiments,the further recombinase enzyme is a serine family recombinase or atyrosine family recombinase. In particular embodiments, the serinefamily recombinase is phiC31, BxB1, HIN invertase, or TN3 resolvase. Inone embodiment, the serine family recombinase is BxB1. In particularembodiments, the tyrosine family recombinase is bacteriophage lambdaintegrase, Cre, or Flp. In certain embodiments, the further recombinaseenzyme is selected from the integrases shown in Table 2.

In certain embodiments, the second chimeric polypeptide includes anantibody or antibody fragment. In one embodiment, the antibody is anIgG. In certain embodiments, the second chimeric polypeptide includes aCAR. In particular embodiments, the further polypeptide includes aCD3-zeta transmembrane domain, CD28 transmembrane domain, CD3-zetacytoplasmic domain, CD28 cytoplasmic domain, 41 BB cytoplasmic domain,ICOS cytoplasmic domain, FcεRIγ cytoplasmic domain, influenza MP-1cytoplasmic domain, VZV cytoplasmic domain, and/or OX40 cytoplasmicdomain, or any combination or derivative thereof. In certainembodiments, the CAR includes an extracellular binding moiety (e.g., anscFv) capable of binding to an antigen associated with a disease. Inparticular embodiments, the disease is a cell proliferation disorder,such as cancer. In specific embodiments, the antigen is atumor-associated antigen. In one embodiment, the antigen is CD19 and thedisease is acute lymphoblastic leukemia (ALL). In another embodiment,the antigen is Tyro3. In certain embodiments, the further polypeptideincludes a ubiquitin ligase domain. In certain embodiments, the furtherpolypeptide includes a knocksideways prey domain. In one embodiment, thefurther polypeptide includes a ubiquitin ligase domain and aknocksideways prey domain.

In some embodiments of any of the first through fifth aspects, an mRNAtranscript encoding the first polypeptide, the second polypeptide,and/or the chimeric polypeptide is capable of being edited by an ADARenzyme. In certain embodiments, the editing includes activation of acryptic splice site in the mRNA transcript to remove an exon from thetranscript. In various embodiments, the editing includes removal of asplice site in the mRNA transcript. In certain embodiments, the mRNAtranscript includes a first region and a second region capable ofhybridizing to the first region to form a duplex. In one embodiment, thefirst region is complementary to the second region, and the duplex is atleast 100 bp in length. In another embodiment, the duplex is no morethan 30 bp in length and includes an editing-site complementarysequence. In a further embodiment, the duplex is greater than 30 bp inlength and includes one or more mismatched bases, bulges, or loops. Incertain embodiments, the first vector or the second vector furtherincludes a polynucleotide encoding an ADAR enzyme.

In some embodiments of any of the first through fifth aspects, an mRNAtranscript encoding the first polypeptide, the second polypeptide,and/or the chimeric polypeptide includes one or more translationalbypassing elements (byps).

In a sixth aspect, the invention features a composition including:

-   -   (a) a first vector including a first polynucleotide encoding a        first polypeptide, the first polynucleotide including a first        site-specific recombination motif;    -   (b) a second vector including a second site-specific        recombination motif and a second polynucleotide encoding a        second polypeptide; and    -   (c) a recombinase enzyme capable of recombining the first        site-specific recombination motif with the second site-specific        recombination motif;

in which the recombining results in formation of a recombinant vectorencoding a chimeric polypeptide including:

-   -   i. the first polypeptide, or a portion thereof, and    -   ii. the second polypeptide, or a portion thereof.

In some embodiments of the sixth aspect, the first polypeptide-encodingregion of the first polynucleotide includes the first site-specificrecombination motif. In some embodiments, the first polypeptide includesa linker, and the portion of the polynucleotide encoding the linkerincludes the first site-specific recombination motif. In certainembodiments, the first vector or the second vector includes apolynucleotide encoding the recombinase enzyme. In various embodiments,the composition further includes an additional vector including apolynucleotide encoding the recombinase enzyme.

In a seventh aspect, the invention features a composition including:

-   -   (a) a first vector including a first polynucleotide encoding a        first polypeptide, the first polynucleotide including an intron        including a first site-specific recombination motif;    -   (b) a second vector including a second site-specific        recombination motif and a second polynucleotide encoding a        second polypeptide; and    -   (c) a recombinase enzyme capable of recombining the first        site-specific recombination motif with the second site-specific        recombination motif;

in which the recombining results in formation of a recombinant vectorencoding a chimeric polypeptide including:

-   -   i. the first polypeptide, or a portion thereof, and    -   ii. the second polypeptide, or a portion thereof.

In some embodiments of the seventh aspect, the portion of the firstpolynucleotide encoding the first polypeptide includes the intron. Inother embodiments of the seventh aspect, the portion of the firstpolynucleotide encoding the first polypeptide does not include theintron.

In certain embodiments, the first vector or the second vector includes apolynucleotide encoding the recombinase enzyme. In further embodiments,the composition includes an additional vector including a polynucleotideencoding the recombinase enzyme.

In an eighth aspect, the invention features a composition including:

-   -   (a) a first vector including a first polynucleotide encoding a        first polypeptide including a first site-specific recombination        motif and an alternate site-specific recombination motif, and    -   (b) (i) a second vector including a second site-specific        recombination motif and a second polynucleotide encoding a        second polypeptide; and a recombinase enzyme capable of        recombining the first site-specific recombination motif with the        second site-specific recombination motif, or    -   (ii) a third vector including a third site-specific        recombination motif distinct from the first site-specific        recombination motif and an alternate polynucleotide encoding an        alternate polypeptide; and an alternate recombinase enzyme        capable of recombining the alternate site-specific recombination        motif with the third site-specific recombination motif;

in which the recombining of the first vector and the second vector bythe recombinase enzyme results in formation of a recombinant vectorencoding a chimeric polypeptide including the first polypeptide, or aportion thereof, and the second polypeptide; and

in which the recombining of the first vector and the third vector by thealternate recombinase enzyme results in formation a recombinant vectorencoding a chimeric polypeptide including the first polypeptide, or aportion thereof, and the alternate polypeptide.

In some embodiments of the eighth aspect, the first polynucleotideincludes the first site-specific recombination motif. In certainembodiments, the first polynucleotide includes an intron including thefirst site-specific recombination motif. In particular embodiments, thefirst vector or the second vector includes a polynucleotide encoding therecombinase enzyme, and/or the first vector or the third vector includesa polynucleotide encoding the alternate recombinase enzyme.

In an ninth aspect, the invention features a composition including:

-   -   (a) a first vector including a first polynucleotide encoding an        scFv including a light chain variable domain, a linker region,        and a heavy chain variable domain, the portion of the first        polynucleotide encoding the linker region including a first        site-specific recombination motif (e.g., an attP site);    -   (b) a second vector including a second site-specific        recombination motif and a second polynucleotide encoding a        second polypeptide; and    -   (c) a recombinase enzyme capable of recombining the first        site-specific recombination motif with the second site-specific        recombination motif;

in which recombination of the first vector with the second vector by therecombinase enzyme forms a recombinant vector encoding a chimericbinding moiety including:

-   -   i. the light chain variable domain and/or the heavy chain        variable domain, and    -   ii. the second polypeptide, or a portion thereof.

In some embodiments of any of the sixth through ninth aspects, the firstpolypeptide is an antibody or antibody fragment. In certain embodiments,the antibody or antibody fragment is a human, mouse, goat, sheep,rabbit, chicken, guinea pig, hamster, horse, or rat antibody or antibodyfragment. In particular embodiments, the antibody is an IgG, IgA, IgD,IgE, IgM, or intrabody. In one embodiment, the antibody is an IgG.

In certain embodiments, the antibody fragment is an scFv, sdAb, dAb,Fab, Fab′, Fab′2, F(ab′)2, Fd, Fv, Feb, or SMIP. In particularembodiments, the antibody fragment is an scFv. In specific embodiments,the scFv is a cytosol-stable scFv. In one embodiment, the scFv is abovine or camelid scFv. In one embodiment, the sdAb is a camelid VHH. Inparticular embodiments, the scFv includes a linker positioned betweenthe light chain variable domain and the heavy chain variable domain ofthe scFv, the linker including the first site-specific recombinationmotif. In various embodiments, the chimeric polypeptide includes thelight chain variable domain of the scFv and/or the heavy chain variabledomain of the scFv.

In some embodiments of any of the sixth through ninth aspects, the firstpolypeptide is a chimeric antigen receptor (CAR). In certainembodiments, the first polypeptide includes a CD8 transmembrane domain,CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmic domain, and/or CD28cytoplasmic domain. In particular embodiments, the chimeric polypeptideincludes the CD8 transmembrane domain, CD3-zeta cytoplasmic domain, 4-1BB cytoplasmic domain, and/or CD28 cytoplasmic domain of the firstpolypeptide. In certain embodiments, the chimeric polypeptide furtherincludes a peptide linker domain positioned between: (i) the CD8transmembrane domain, CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmicdomain, and/or CD28 cytoplasmic domain of the first polypeptide, and(ii) the first polypeptide, or the portion thereof. In particularembodiments, the peptide linker domain has a length of about 0-250 aminoacids or about 1-250 amino acids (e.g., about 1-50, 1-10, 10-20, 20-50,or 50-100 amino acids). In a preferred embodiment, the peptide linkerdomain has a length of about 1-50 amino acids. In certain embodiments,the CAR includes an extracellular binding moiety (e.g., an scFv) capableof binding to an antigen associated with a disease. In particularembodiments, the disease is a cell proliferation disorder, such ascancer. In specific embodiments, the antigen is a tumor-associatedantigen. In one embodiment, the antigen is CD19 and the disease is acutelymphoblastic leukemia (ALL).

In some embodiments of any of the sixth through ninth aspects, thechimeric polypeptide is an antibody or antibody fragment. In certainembodiments, the antibody or antibody fragment is a human, mouse, goat,sheep, rabbit, chicken, guinea pig, hamster, horse, or rat antibody orantibody fragment. In particular embodiments, the antibody is an IgG,IgA, IgD, IgE, IgM, or intrabody. In a specific embodiment, the antibodyis an IgG. In one embodiment, the first polypeptide includes thevariable light chain and/or variable heavy chains of the IgG. Inparticular embodiments, the first vector includes a polynucleotideencoding a constant domain of the IgG. In specific embodiments, theconstant domain includes a CL domain or an Fc domain. In on embodiment,the constant domain includes a CH domain including the Fc domain.

In certain embodiments, the antibody fragment is an scFv, dAb, Fab,Fab′, Fab′2, F(ab′)2, Fd, Fv, Feb, or SMIP. In a particular embodiment,the antibody fragment is an scFv. In a specific embodiment, the scFv isa cytosol-stable scFv. In one embodiment, the scFv is a bovine orcamelid scFv.

In some embodiments of any of the sixth through ninth aspects, thechimeric polypeptide is a chimeric antigen receptor (CAR). In certainembodiments, the second polypeptide includes a CD8 transmembrane domain,CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmic domain, and/or CD28cytoplasmic domain. In particular embodiments, the first polypeptide isan scFv and the chimeric polypeptide includes the light chain variabledomain of the scFv and the CD8 transmembrane domain, CD3-zetacytoplasmic domain, 4-1 BB cytoplasmic domain, and/or CD28 cytoplasmicdomain. In certain embodiments, the chimeric polypeptide furtherincludes a peptide linker domain positioned between: (i) the light chainvariable domain of the scFv, and (ii) the CD8 transmembrane domain,CD3-zeta cytoplasmic domain, 4-1 BB cytoplasmic domain, and/or CD28cytoplasmic domain. In particular embodiments, the peptide linker domainhas a length of about 0-250 amino acids or about 1-250 amino acids(e.g., about 1-50, 1-10, 10-20, 20-50, or 50-100 amino acids). In apreferred embodiment, the peptide linker domain has a length of about1-50 amino acids. In other embodiments, the first polypeptide is an scFvand the chimeric polypeptide includes the heavy chain variable domain ofthe scFv and the CD8 transmembrane domain, CD3-zeta cytoplasmic domain,4-1 BB cytoplasmic domain, and/or CD28 cytoplasmic domain. In certainembodiments, the chimeric polypeptide further includes a peptide linkerdomain positioned between: (i) the heavy chain variable domain of thescFv, and (ii) the CD8 transmembrane domain, CD3-zeta cytoplasmicdomain, 4-1 BB cytoplasmic domain, and/or CD28 cytoplasmic domain. Inparticular embodiments, the peptide linker domain has a length of about0-250 amino acids or about 1-250 amino acids (e.g., about 1-50, 1-10,10-20, 20-50, or 50-100 amino acids). In a preferred embodiment, thepeptide linker domain has a length of about 1-50 amino acids. In furtherembodiments, the first polypeptide is an scFv and the chimericpolypeptide includes the heavy chain variable domain and the light chainvariable domain of the scFv and the CD8 transmembrane domain, CD3-zetacytoplasmic domain, 4-1 BB cytoplasmic domain, and/or CD28 cytoplasmicdomain. In certain embodiments, the chimeric polypeptide furtherincludes a peptide linker domain positioned between: (i) the heavy chainvariable domain and the light chain variable domain of the scFv, and(ii) the CD8 transmembrane domain, CD3-zeta cytoplasmic domain, 4-1 BBcytoplasmic domain, and/or CD28 cytoplasmic domain. In particularembodiments, the peptide linker domain has a length of about 0-250 aminoacids or about 1-250 amino acids (e.g., about 1-50, 1-10, 10-20, 20-50,or 50-100 amino acids). In a preferred embodiment, the peptide linkerdomain has a length of about 1-50 amino acids. In certain embodiments,the CAR includes an extracellular binding moiety (e.g., an scFv) capableof binding to an antigen associated with a disease. In particularembodiments, the disease is a cell proliferation disorder, such ascancer. In specific embodiments, the antigen is a tumor-associatedantigen. In one embodiment, the antigen is CD19 and the disease is acutelymphoblastic leukemia (ALL).

In some embodiments of any of the sixth through ninth aspects, thechimeric polypeptide includes an ubiquitin ligase domain. In certainembodiments, the second polypeptide includes the ubiquitin ligasedomain. In particular embodiments, the ubiquitin ligase domain includesa CHIPΔTPR domain.

In some embodiments of any of the sixth through ninth aspects, thechimeric polypeptide includes a knocksideways prey domain. In certainembodiments, the second polypeptide includes the knocksideways preydomain. In one embodiment, the knocksideways prey domain includes anFKBP domain.

In certain embodiments, the composition further includes a knocksidewaysbait protein. In a particular embodiment, the knocksideways bait proteinincludes an FRB domain. In specific embodiments, the knocksideways baitprotein includes a mitochondrial outer membrane targeting signal. In oneembodiment, the knocksideways bait protein is a Mitotrap protein.

In certain embodiments, the chimeric polypeptide further includes aubiquitin ligase domain (e.g., a chimeric polypeptide including aknocksideways prey domain and a ubiquitin ligase domain). In aparticular embodiment, the second polypeptide includes the ubiquitinligase domain. In one embodiment, the ubiquitin ligase domain includes aCHIPΔTPR domain.

In some embodiments of any of the sixth through ninth aspects, therecombinase enzyme is a serine family recombinase or a tyrosine familyrecombinase. In certain embodiments, the serine family recombinase isphiC31, BxB1, HIN invertase, or TN3 resolvase. In one embodiment, theserine family recombinase is phiC31. In certain embodiments, thecomposition further includes an accessory factor. In one embodiment, theaccessory factor includes Xis. In further embodiments, the tyrosinefamily recombinase is bacteriophage lambda integrase, Cre, or Flp. Inparticular embodiments, the recombinase enzyme is selected from theintegrases shown in Table 2.

In some embodiments of any of the sixth through ninth aspects, the firstpolypeptide, the second polypeptide, and/or the chimeric polypeptideincludes a marker. In certain embodiments, the marker is an epitope tagand/or a fluorescent protein. In particular embodiments, the epitope tagis a FLAG, HA, Myc, V5, His, GST, MBP, AviTag, or streptavidin tag, orany other epitope tag known in the art. In particular embodiments, thefluorescent protein is EGFP, GFP, YFP, CFP, mCherry, dsRed, or any otherfluorescent protein known in the art.

In some embodiments of any of the sixth through ninth aspects, thecomposition further includes a cell including the vectors and therecombinase enzyme. In particular embodiments, the cell is included inan emulsion droplet. In certain embodiments, the first vector is aplasmid or a phagemid. In particular embodiments, the first vectorincludes a polynucleotide encoding a display protein. In specificembodiments, the display protein is capable of displaying the firstpolypeptide, or a portion thereof, on the extracellular surface of acell (e.g., the cell in which the recombining step takes place). In oneembodiment, the display protein includes ompA. In another embodiment,the display protein includes bclA. In certain embodiments, the cell is abacterial cell. In one embodiment, the bacterial cell is E. coli. Inother embodiments, the cell is a eukaryotic cell. In particularembodiments, the eukaryotic cell is a mammalian cell or an insect cell.In certain embodiments, the cell further includes a vector including apolynucleotide encoding the recombinase enzyme. In further embodiments,the cell further includes a chromosome including a polynucleotideencoding the recombinase enzyme.

In some embodiments of any of the sixth through ninth aspects, thevectors and the recombinase enzyme (e.g., phiC31 or bacteriophage lambdaintegrase) are located within a cell-free system. In one embodiment, therecombinase enzyme is bacteriophage lambda integrase. In certainembodiments, the cell free system is included in an emulsion droplet.

In some embodiments of any of the sixth through ninth aspects, the firstvector includes a plurality of distinct regulatory elements positionedadjacent to each other. In certain embodiments, one of the regulatoryelements controls the expression of the first polypeptide, or a portionthereof, in a first cell type, and another of the regulatory elementscontrols the expression of the first polypeptide, or a portion thereof,in a second cell type. In particular embodiments, the first polypeptide,or portion thereof is fused to a protein fragment when expressed in thefirst cell type. In specific embodiments, the protein fragment includesa viral coat protein. In one embodiment, the viral coat protein is M13gpIII. In certain embodiments, the protein fragment further includes abacterial signal peptide.

In some embodiments of any of the sixth through ninth aspects, thesecond vector includes a plurality of distinct regulatory elementspositioned adjacent to each other. In certain embodiments, one of theregulatory elements controls the expression of the second polypeptide,or a portion thereof, in a first cell type, and another of theregulatory elements controls the expression of the second polypeptide,or a portion thereof, in a second cell type. In particular embodiments,the second polypeptide, or portion thereof is fused to a proteinfragment when expressed in the first cell type. In specific embodiments,the protein fragment includes a viral coat protein. In one embodiment,the viral coat protein is M13 gpIII. In certain embodiments, the proteinfragment further includes a bacterial signal peptide.

In some embodiments of any of the sixth through ninth aspects, therecombinant vector includes a plurality of distinct regulatory elementspositioned adjacent to each other. In certain embodiments one of theregulatory elements controls the expression of the chimeric polypeptidein a first cell type, and another of the regulatory elements controlsthe expression of the chimeric polypeptide in a second cell type. Inparticular embodiments, the first cell type is a bacterial cell, and thesecond cell type is a eukaryotic cell. In one embodiment, the bacterialcell is an E. coli cell. In specific embodiments, the eukaryotic cell isa mammalian cell, insect cell, or fungal cell. In one embodiment, themammalian cell is a human cell. In a further embodiment, the fungal cellis a yeast cell.

In certain embodiments of any of the above, one or more of the distinctregulatory elements is a promoter. In particular embodiments, thepromoter is a bacterial promoter (e.g., a lac promoter, T7 promoter, orT3 promoter). In one embodiment, the bacterial promoter is a lacpromoter. In other embodiments, the promoter is a eukaryotic promoter(e.g., a promoter capable of controlling expression in a mammalian cell,an insect cell, or a fungal cell). In one embodiment, the promotercapable of controlling expression in a mammalian cell is a CMV promoteror an EF1a promoter. In another embodiment, the promoter capable ofcontrolling expression in an insect cell is a polyhedron promoter.

In some embodiments of any of the sixth through ninth aspects, the firstpolynucleotide includes an intron including an intronic regulatoryelement. In certain embodiments, the intronic regulatory elementcontrols the expression of the first polypeptide, or a portion thereof,in a prokaryotic cell. In a particular embodiment, the prokaryotic cellis a bacterial cell. In one embodiment, the bacterial cell is E. coli.In certain embodiments, the first polypeptide, or portion thereof, isfused to a protein fragment when expressed in the prokaryotic cell. In aparticular embodiment, the protein fragment includes a viral coatprotein. In one embodiment, the viral coat protein is M13 gpIII. Incertain embodiments, the protein fragment further includes a bacterialsignal peptide. In particular embodiments, the intron further includes apolynucleotide encoding the protein fragment. In various embodiments,the intronic regulatory element controls the expression of the proteinfragment. In certain embodiments, the intronic regulatory element isremoved from the transcript of the first polynucleotide in a eukaryoticcell by RNA splicing. In particular embodiments, the eukaryotic cell isa mammalian cell (e.g., a human cell), insect cell, or fungal cell.

In certain embodiments, the intronic regulatory element is a promoter.In particular embodiments, the promoter is a bacterial promoter (e.g., alac promoter, T7 promoter, or T3 promoter). In one embodiment, thebacterial promoter is a lac promoter. In other embodiments, the promoteris a eukaryotic promoter (e.g., a promoter capable of controllingexpression in a mammalian cell, an insect cell, or a fungal cell). Inone embodiment, the promoter capable of controlling expression in amammalian cell is a CMV promoter or an EF1a promoter. In anotherembodiment, the promoter capable of controlling expression in an insectcell is a polyhedron promoter.

In some embodiments of any of the sixth through ninth aspects, the firstvector further includes a pair of complementary site-specificrecombination motifs (e.g., two loxP sites, two FRT sites, or an attBsite and an attP site). In certain embodiments, the firstpolynucleotide, a fragment thereof, and/or the first site-specificrecombination motif are located between the pair of complementarysite-specific recombination motifs. In some embodiments of any of thesixth through ninth aspects, the second vector further includes a pairof complementary site-specific recombination motifs (e.g., two loxPsites, two FRT sites, or an attB site and an attP site). In certainembodiments, the second polynucleotide, a fragment thereof, and/or thesecond site-specific recombination motif are located between the pair ofcomplementary site-specific recombination motifs.

In certain embodiments, the pair of complementary site-specificrecombination motifs are oriented such that recombination of the pair ofcomplementary site-specific recombination motifs results in theinversion of the intervening sequences. In other embodiments, the pairof complementary site-specific recombination motifs are oriented suchthat recombination of the pair of complementary site-specificrecombination motifs results in the deletion of the interveningsequences. In certain embodiments, the composition further includes arecombinase enzyme (e.g., Cre, FRT, phiC31, or bacteriophage lambdaintegrase) capable of recombining the pair of complementarysite-specific recombination motifs.

In particular embodiments, the pair of complementary site-specificrecombination motifs includes a pair of loxP sites. In one embodiment,the composition further includes a Cre recombinase enzyme.

In other embodiments, the pair of complementary site-specificrecombination motifs includes a pair of FRT sites. In one embodiment,the composition further includes a Flp recombinase enzyme.

In yet further embodiments, the pair of complementary site-specificrecombination motifs includes an attB site and an attP site. In specificembodiments, the composition further includes a phiC31 or BxB1recombinase enzyme suitable for recombining the attB site and the attPsite of the pair of complementary site-specific recombination motifs. Incertain embodiments, the composition further includes a recombinaseenzyme (e.g., phiC31 or BxB1) capable of recombining said firstsite-specific recombination motif and/or said second site-specificrecombination motif, and a distinct recombinase enzyme (e.g., BxB1,phiC31, Cre, or Flp) capable of recombining the pair of complementarysite-specific recombination motifs. In one embodiment, the compositionfurther includes a phiC31 or BxB1 recombinase enzyme suitable forrecombining the attB site and the attP site of the pair of complementarysite-specific recombination motifs.

In some embodiments of any of the sixth through ninth aspects, the firstvector is a viral vector.

In certain embodiments, the first vector is an adenoviral, lentiviral,or baculoviral vector. In further embodiments, the second vector is aviral vector. In certain embodiments, the second vector is anadenoviral, lentiviral, or baculoviral vector. In particularembodiments, one or more viral elements are located within an intron.

In some embodiments of any of the sixth through ninth aspects, the firstvector is a phagemid vector. In other embodiments of any of the sixththrough ninth aspects, the second vector is a phagemid vector.

In some embodiments of any of the sixth through ninth aspects,

the first vector further includes a first recombination motif fragmentand the second vector includes a second recombination motif fragment,and

the recombinant vector includes a cryptic site-specific recombinationmotif including the first recombination motif fragment and the secondrecombination motif fragment,

in which recombining the recombinant vector and a further vectorincluding

-   -   (i) a further site-specific recombination motif, and    -   (ii) a polynucleotide encoding a further polypeptide;        with a further recombinase enzyme capable of recombining the        cryptic site-specific recombination motif with the further        site-specific recombination motif results in formation of a        second recombinant vector encoding a second chimeric polypeptide        including:    -   (i) the chimeric polypeptide, or a portion thereof, and    -   (ii) the further polypeptide, or a portion thereof.

In certain embodiments, the first site-specific recombination motif andthe cryptic site-specific recombination motif are the same. In otherembodiments, the first site-specific recombination motif and the crypticsite-specific recombination motif are different.

In certain embodiments, the further recombinase enzyme is a serinefamily recombinase or a tyrosine family recombinase. In particularembodiments, the serine family recombinase is phiC31, BxB1, HINinvertase, or TN3 resolvase. In one embodiment, the serine familyrecombinase is BxB1. In further embodiments, the tyrosine familyrecombinase is bacteriophage lambda integrase, Cre, or Flp. In certainembodiments, the further recombinase enzyme is selected from theintegrases shown in Table 2.

In certain embodiments, the second chimeric polypeptide includes anantibody or antibody fragment. In one embodiment, the antibody is anIgG. In further embodiments, the second chimeric polypeptide includes aCAR. In particular embodiments, the further polypeptide includes aCD3-zeta transmembrane domain, CD28 transmembrane domain, CD3-zetacytoplasmic domain, CD28 cytoplasmic domain, 41 BB cytoplasmic domain,ICOS cytoplasmic domain, FcεRIγ cytoplasmic domain, influenza MP-1cytoplasmic domain, VZV cytoplasmic domain, and/or OX40 cytoplasmicdomain, or any combination or derivative thereof. In certainembodiments, the CAR includes an extracellular binding moiety (e.g., anscFv) capable of binding to an antigen associated with a disease. Inparticular embodiments, the disease is a cell proliferation disorder,such as cancer. In specific embodiments, the antigen is atumor-associated antigen. In one embodiment, the antigen is CD19 and thedisease is acute lymphoblastic leukemia (ALL). In another embodiment,the antigen is Tyro3. In yet further embodiments, the furtherpolypeptide includes a ubiquitin ligase domain. In additionalembodiments, the further polypeptide includes a knocksideways preydomain. In a specific embodiment, the further polypeptide includes aubiquitin ligase domain and a knocksideways prey domain.

In some embodiments of any of the sixth through ninth aspects, thecomposition further includes an mRNA transcript encoding the firstpolypeptide, the second polypeptide, and/or the chimeric polypeptide, inwhich the mRNA transcript is capable of being edited by an ADAR enzyme.In certain embodiments, the editing includes activation of a crypticsplice site in the mRNA transcript to remove an exon from thetranscript. In various embodiments, the editing includes removal of asplice site in the mRNA transcript. In particular embodiments, the mRNAtranscript includes a first region and a second region capable ofhybridizing to the first region to form a duplex. In one embodiment, thefirst region is complementary to the second region, and the duplex is atleast 100 bp in length. In another embodiment, the duplex is no morethan 30 bp in length and includes an editing-site complementarysequence. In an alternate embodiment, the duplex is greater than 30 bpin length and includes one or more mismatched bases, bulges, or loops.In certain embodiments, the first vector or the second vector furtherincludes a polynucleotide encoding an ADAR enzyme.

In some embodiments of any of the sixth through ninth aspects, thecomposition further includes an mRNA transcript encoding the firstpolypeptide, the second polypeptide, and/or the chimeric polypeptide, inwhich the mRNA transcript includes one or more translational bypassingelements (byps).

In some embodiments of any of the sixth through ninth aspects, the firstvector includes a promoter capable of controlling expression of thefirst polypeptide in a bacterial cell (e.g., E. coli). In someembodiments of any of the sixth through ninth aspects, the first vectorincludes a promoter capable of controlling expression of the firstpolypeptide in a eukaryotic cell (e.g., a mammalian cell, such as ahuman cell; an insect cell; or a fungal cell, such as a yeast cell). Incertain embodiments, the first vector includes a promoter capable ofcontrolling expression of the first polypeptide in a bacterial cell(e.g., E. coli) and a promoter capable of controlling expression of thefirst polypeptide in a eukaryotic cell (e.g., a mammalian cell, such asa human cell; an insect cell; or a fungal cell, such as a yeast cell).

In some embodiments of any of the sixth through ninth aspects, thesecond vector includes a promoter capable of controlling expression ofthe second polypeptide in a bacterial cell (e.g., E. coli). In someembodiments of any of the sixth through ninth aspects, the second vectorincludes a promoter capable of controlling expression of the secondpolypeptide in a eukaryotic cell (e.g., a mammalian cell, such as ahuman cell; an insect cell; or a fungal cell, such as a yeast cell). Incertain embodiments, the second vector includes a promoter capable ofcontrolling expression of the second polypeptide in a bacterial cell(e.g., E. coli) and a promoter capable of controlling expression of thesecond polypeptide in a eukaryotic cell (e.g., a mammalian cell, such asa human cell; an insect cell; or a fungal cell, such as a yeast cell).In certain embodiments of any of the above, the promoter capable ofcontrolling expression of the first or second polypeptide in a bacterialcell is a lac promoter, T7 promoter, or T3 promoter. In certainembodiments of any of the above, the promoter capable of controllingexpression of the first or second polypeptide in a mammalian cell is aCMV promoter or an EF1a promoter. In certain embodiments of any of theabove, the promoter capable of controlling expression of the first orsecond polypeptide in an insect cell is a polyhedron promoter.

In some embodiments of any of the sixth through ninth aspects, theportion of the first vector encoding the first polypeptide, or a portionthereof, further encodes a fusion to a protein fragment. In specificembodiments, the protein fragment includes a viral coat protein. In oneembodiment, the viral coat protein is M13 gpIII. In certain embodiments,the protein fragment further includes a bacterial or mammalian signalpeptide.

In some embodiments of any of the sixth through ninth aspects, theportion of the second vector encoding the second polypeptide, or aportion thereof, further encodes a fusion to a protein fragment. Inspecific embodiments, the protein fragment includes a viral coatprotein. In one embodiment, the viral coat protein is M13 gpIII. Incertain embodiments, the protein fragment further includes a bacterialor mammalian signal peptide.

In some embodiments of any of the sixth through ninth aspects, the firstsite-specific recombination motif is positioned upstream of (e.g., 5′to) the first polynucleotide. In certain embodiments, the firstsite-specific recombination motif is positioned upstream of (e.g., 5′to) a polynucleotide encoding a marker (e.g., a resistance marker, suchas a chloramphenicol (CAM) gene, ampR gene, or any other markerdescribed herein). In certain embodiments, the second site-specificrecombination motif is positioned between a regulatory element (e.g., apromoter) and the second polynucleotide. In one embodiment, theregulatory element controls expression of the second polynucleotide. Inparticular embodiments, the second site-specific recombination motif ispositioned between a regulatory element (e.g., a promoter, such as abacterial promoter, e.g., a CAM resistance gene promoter) and apolynucleotide encoding a recombinase enzyme (e.g., phiC31,bacteriophage lambda integrase, BxB1, Cre, or Flp). In a specificembodiment, the regulatory element does not control expression of therecombinase enzyme. In one embodiment, the regulatory element controlsexpression of the marker. In a preferred embodiment, the recombinantvector includes, in order, the promoter and the polynucleotide encodingthe marker, such that the promoter controls expression of the markerfrom the recombinant vector.

In some embodiments of any of the sixth through ninth aspects, thesecond site-specific recombination motif is positioned upstream of(e.g., 5′ to) the second polynucleotide. In certain embodiments, thesecond site-specific recombination motif is positioned upstream of(e.g., 5′ to) a polynucleotide encoding a marker (e.g., a resistancemarker, such as a CAM gene, ampR gene, or any other marker describedherein). In certain embodiments, the first site-specific recombinationmotif is positioned between a regulatory element (e.g., a promoter) andthe first polynucleotide. In one embodiment, the regulatory elementcontrols expression of the first polynucleotide. In particularembodiments, the first site-specific recombination motif is positionedbetween a regulatory element (e.g., a promoter, such as a CAM promoter)and a polynucleotide encoding a recombinase enzyme (e.g., phiC31,bacteriophage lambda integrase, BxB1, Cre, or Flp). In a specificembodiment, the regulatory element does not control expression of therecombinase enzyme. In one embodiment, the regulatory element controlsexpression of the marker. In a preferred embodiment, the recombinantvector includes, in order, the promoter and the polynucleotide encodingthe marker, such that the promoter controls expression of the markerfrom the recombinant vector.

In a tenth aspect, the invention features a kit including any of thecompositions described herein (e.g., a composition of the sixth throughtenth aspects) and instructions for producing a chimeric polypeptideaccording to any of the methods described herein (e.g., a method of thefirst through fifth aspects).

In an eleventh aspect, the invention features a method of converting asingle-chain variable fragment (scFv) into an immunoglobulin G (IgG)antibody, comprising

(a) providing a first phagemid vector comprising, in order from 5′ to3′,

-   -   a first Mammalian expression control motif,    -   optionally, a first 5′ mammalian splice site (Mam5′SS),    -   a first E. coli expression control motif,    -   optionally, a first 3′ mammalian splice site (Mam3′SS),    -   a sequence encoding a heavy chain variable region (VH) of the        scFv,    -   optionally, a second 5′ mammalian splice site (Mam_(5′SS)),    -   a first site-specific recombination motif,    -   optionally, a second 3′ mammalian splice site (Mam_(3′SS)),    -   a sequence encoding a light chain variable region (VL) of the        scFv,    -   a third 5′ mammalian splice site (Mam_(5′SS)),    -   a fusion display protein sequence    -   a third 3′ mammalian splice site (Mam_(3′SS)),    -   a sequence encoding a light chain constant region (CL),

(b) providing a second phagemid vector comprising, in order from 5′ to3′,

-   -   a second Mammalian expression control motif    -   optionally, a fourth 5′ mammalian splice site (Mam5′SS),    -   a second site-specific recombination motif,    -   optionally, a fourth 3′ mammalian splice site (Mam3′SS);    -   a sequence encoding a fragment crystallizable (Fc) region (e.g.,        a region encoding a CH region); and

c) contacting the first phagemid vector and the second phagemid vectorin the presence of a recombinase,

wherein the recombinase combines the first phagemid vector and thesecond phagemid vector in a site-specific manner to form an integrantvector,

wherein the integrant vector expresses the VL fused to the CL and aseparate VH fused to a polypeptide domain including the Fc (e.g., the CHregion) to form an IgG,

thereby upon expression converting a scFv into an IgG antibody.

In a twelfth aspect, the invention features a method of converting asingle-chain variable fragment (scFv) into a CAR, comprising

(a) providing a first phagemid vector comprising, in order from 5′ to3′,

-   -   a first Mammalian expression control motif,    -   optionally, a first 5′ mammalian splice site (Mam5′SS),    -   a first E. coli expression control motif,    -   optionally, a first 3′ mammalian splice site (Mam3′SS),    -   a sequence encoding a heavy chain variable region (VH) of the        scFv,    -   optionally, a second 5′ mammalian splice site (Mam_(5′SS)),    -   a first site-specific recombination motif,    -   optionally, a second 3′ mammalian splice site (Mam_(3′SS)),    -   a sequence encoding a light chain variable region (VL) of the        scFv,    -   a third 5′ mammalian splice site (Mam_(5′SS)),    -   a fusion display protein sequence    -   a third 3′ mammalian splice site (Mam_(3′SS)),    -   a sequence encoding a light chain constant region (CL),

(b) providing a second phagemid vector comprising, in order from 5′ to3′,

-   -   a second site-specific recombination motif, and    -   a sequence encoding a TCRζ region; and

c) contacting the first phagemid vector and the second phagemid vectorin the presence of a recombinase,

wherein the recombinase combines the first phagemid vector and thesecond phagemid vector in a site-specific manner to form an integrantvector,

wherein the integrant vector expresses the VL fused to the CL and aseparate VH fused to the TCRζ region to form a CAR,

thereby upon expression converting a scFv into an IgG antibody.

In some embodiments of the eleventh and twelfth aspects, the firstphagemid vector includes a first termination codon between the third 5′mammalian splice site and the fusion display protein sequence and/or asecond termination codon between the fusion display protein sequence andthe third 3′ mammalian splice site. In certain embodiments, theintegrant vector is capable of expressing a selectable marker. Inparticular embodiments, the integrant vector is only capable ofexpressing the selectable marker after integration occurs.

Definitions

By “chimeric polypeptide” is meant a polypeptide including a fusion ofat least two polypeptides and/or polypeptide fragments thereof. Achimeric polypeptide may include two or more distinct domains, eachincluding at least one of the polypeptides (or a portion thereof) orpolypeptide fragments. In some instances, a chimeric polypeptideincludes an antigen-determining region of a binding moiety (e.g., anantibody variable domain) fused to a polypeptide domain with a desiredfunctionality (e.g., an antibody constant domain, a CD3-zeta domain, aubiquitin ligase domain, or a knocksideways prey domain). Apolynucleotide (e.g., a vector) encoding a chimeric polypeptide can begenerated according to the recombination methods described herein. Forexample, a chimeric polypeptide can be encoded by a polynucleotide inwhich the coding sequence of a first polypeptide, or a portion thereof,is attached to the coding sequence of a second polypeptide (or afragment thereof), e.g., by recombination according to the methods ofthe present invention. Exemplary chimeric polypeptides include IgGsgenerated by fusing a variable domain (e.g., one or more VH or VLdomains) from an antibody or antibody fragment (e.g., an scFv) to aconstant domain (e.g., one or more CH or CL domains), chimeric antigenreceptors (CARs) generated by fusing a variable domain from an antibody(e.g., one or more VH or VL domains) to a heterologous transmembranedomain and cytoplasmic domain (e.g., a CD3-zeta domain), and fusionsbetween a binding moiety (or a portion thereof) and a ubiquitin ligasedomain or knocksideways prey domain.

“Polypeptide fragment,” as used herein, means any amino acid sequencethat is less than a full-length wild-type polypeptide. A polypeptidefragment of the invention can include one or more of, for example, anantigen-determining region (e.g., an antibody variable domain), astructural domain (e.g., an antibody constant domain), a framework(e.g., as described herein), a transmembrane domain (e.g., a CD3-zetatransmembrane domain), a domain capable of signal transduction (e.g., aCD3-zeta cytoplasmic domain), a domain having a desired function (e.g.,a ubiquitin ligase domain or knocksideways prey domain), or any otherpolypeptide portion known in the art. In some instances, apolynucleotide encoding a polypeptide fragment can be present on avector (e.g., a first vector or a second vector). In certain instances,the polynucleotide encoding the polypeptide fragment can be conjugatedto another polynucleotide encoding a polypeptide (e.g., a firstpolypeptide, a second polypeptide, or a fragment thereof) byrecombination of the vector with a vector including the otherpolynucleotide according to the methods of the invention.

“Recombinant vector” or “integrant vector” means a polynucleotide vectorformed by recombination of two parent vectors (e.g., a first vector anda second vector of the invention). The parent vectors to be recombinedmay each include a site-specific recombination motif, such that the twosite-specific recombination motifs can be recombined by a recombinaseenzyme to attach at least a portion of one vector to at least a portionof the other, thereby forming the new recombinant vector. A recombinantvector may include one or more polynucleotides encoding the same ordifferent polypeptides from those of the parent vectors. In someinstances, a polynucleotide encoding a first polypeptide, or a fragmentthereof (e.g., an antigen-determining region, such as a variable domainfrom an antibody or an antibody fragment), from one parent vector (e.g.,a first vector of the invention) can be attached to a polynucleotideencoding a second polypeptide (e.g., a framework, such as a constantregion from an antibody or antibody fragment; a CAR transmembrane and/orcytoplasmic domain; a ubiquitin ligase domain; and/or a knocksidewaysprey domain), or a fragment thereof, from the other vector to form apolynucleotide in the recombinant vector that encodes a chimericpolypeptide, which includes both the polypeptide, or a fragment thereof,from the first parent vector and the second polypeptide, or a fragmentthereof, from the second parent vector.

“Binding moiety” means an agent capable of binding a target molecule,for example, a target protein, such as an antigen. In some instances, abinding moiety is a protein, polypeptide, polypeptide fragment, nucleicacid, polysaccharide, small molecule, aptamer, or any combinationthereof. A particular binding moiety is a “cognate” to a target if it iscapable of binding that target. A binding moiety can, in some instances,include one or more subunits (e.g., one or more of the same subunit, orone or more distinct subunits), e.g., such that the subunits must be inclose physical proximity for the binding moiety to function. In certaininstances in which a binding moiety is composed of multiple subunits,the subunits may be brought into close proximity by the interaction oftwo or more of the subunits. Exemplary binding moieties include, withoutlimitation, antibodies, antibody fragments, and binding proteins, orfragments thereof.

“Antibody” means any form of immunoglobulin, heavy chain antibody, lightchain antibody, LRR-based antibody, or other protein scaffold withantibody-like properties, as well as any other immunological bindingmoiety known in the art, including antibody fragments (e.g., a Fab,Fab′, Fab′2, F(ab′)₂, Fd, Fv, Feb, scFv, or SMIP). The subunitstructures and three-dimensional configurations of different classes ofantibodies are known in the art.

“Antibody fragment” means a binding moiety that includes a portionderived from or having significant homology to an antibody, such as theantigen-determining region of an antibody. Exemplary antibody fragmentsinclude Fab, Fab′, Fab′2, F(ab′)2, Fd, Fv, Feb, scFv, and SMIP.

By “chimeric antigen receptor” (CAR) is meant a polypeptide bindingmoiety including a binding moiety portion, a transmembrane domain, and acytoplasmic domain, in which binding of a ligand to the binding moietyportion results in activation of a downstream signaling pathway by thecytoplasmic domain. In some instances, the binding moiety portion is anantibody or antibody fragment (e.g., an scFv). In certain instances, thetransmembrane domain and/or cytoplasmic domain are derived frommembrane-bound receptors expressed by an immune cell (e.g., a T cell).For example, the transmembrane domain and/or cytoplasmic domain may bederived from CD8 (e.g., the hinge and/or transmembrane domain of CD8),CD3-zeta and/or CD28. The cytoplasmic domain may include one or morepolypeptide domains capable of transmitting activation signals to theimmune cell (e.g., the T cell). For example, the polypeptide domains caninclude a CD3-zeta cytoplasmic domain, a CD28 cytoplasmic domain, a 4-1BB cytoplasmic domain, an OX40 domain, an ICOS domain, and/or anycombination or derivative thereof. A CAR, or portions thereof, can befused to another polypeptide (e.g., a binding moiety) according to therecombination methods of the invention.

“Ubiquitin ligase domain,” as used herein, means a polypeptide domaincapable of catalyzing the transfer of ubiquitin to a polypeptidesubstrate. A ubiquitin ligase domain can be fused to another polypeptide(e.g., a binding moiety) according to the recombination methods of theinvention. In some instances, ubiquitin ligase domains useful in themethods and compositions of the invention include E3 ligase domains(e.g., C-terminus of Hsc70 Interacting Protein (CHIP) E3 ligase).Ubiquitin ligases and uses thereof, e.g., for targeted proteinsilencing, are described, for example, in Portnoff et al. (J. Biol.Chem. 289: 7844-7855, 2014), incorporated by reference herein in itsentirety.

“Knocksideways prey domain” means a polypeptide domain that can be usedfor rapid inactivation of a target protein by sequestering the targetprotein to an intracellular region, for example, as described inRobinson and Hirst (Curr. Protoc. Cell Biol. 61:15.20.1-15.20.7, 2013)and Robinson et al. (Dev. Cell 18: 324-331, 2010), each of which isincorporated by reference herein in its entirety. In some instances, aknocksideways prey domain can bind to a knocksideways bait protein inthe presence of a particular small molecule (e.g., rapamycin or arapamycin analogue). In certain instances, a knocksideways prey domainincludes a binding domain that recognizes a target protein to besequestered (e.g., a binding moiety of the invention) and a secondbinding domain that recognizes the small molecule, such that thepresence of the small molecule results in the formation of a complexincluding the knocksideways prey domain, the target protein, the smallmolecule, and the knocksideways bait protein. The knocksideways baitprotein may, in some instances, be attached to an intracellularorganelle (e.g., a mitochondrion), such that the formation of thecomplex results in sequestration of the target protein to theintracellular organelle. In certain embodiments, the knocksideways baitprotein includes an FRB domain, the knocksideways prey domain includesan FKBP domain, and the small molecule is rapamycin or a derivativethereof. In one embodiment, the knocksideways bait protein is a Mitotrapprotein, as described in Robinson and Hirst, supra.

“Fusion protein” means a single protein or polypeptide that includes twoprotein or polypeptide segments joined together. Generally, the twoprotein or polypeptide segments are not naturally joined together.

“Linker,” as used herein, means a peptide that connects two polypeptideregions. A linker may be, for example, 0-100 amino acids in length(e.g., about 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 20,25, 30, 40, 50, 75, or 100 amino acids in length). A linker may includea stalk region (e.g., a stalk region including a site-specificrecombination motif, such as an attB site or an attP site). The stalkmay be of any length suitable for placing distance between the twolinked polypeptide regions (e.g., about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,11, 12, 13, 14, 15, 20, 21, 22, 23, 24, 25, 30, 40, 50, 75, or 100 aminoacids in length, or more). In some instances, a linker connects twosegments of a fusion protein. In some instances, a linker connects twoantigen-determining regions of a binding moiety (e.g., variable domainsof an antibody or antibody fragment). In one embodiment, a linkerconnects the heavy chain variable domain of an scFv to the light chainvariable domain.

“Constant region” means a portion of a binding moiety (e.g., an antibodyor antibody fragment) that is substantially conserved across bindingmoieties of a particular type or group. The identification of bindingmoiety constant regions, in some instances referred to as constantdomains, is well known in the art.

“Framework,” as used herein, means a set of one or more constant regionsof a particular type or group of polypeptides (e.g., binding moieties),or a portion thereof, optionally in an arrangement characteristic ofthat type or group of binding moiety. In some instances, a frameworkincludes an antibody framework region (e.g., a region in the variabledomain of an antibody outside of and having less variability than thecomplementarity determining regions). In other instances, a frameworkincludes a constant region of an antibody (e.g., an immunoglobulin lightchain constant region or an immunoglobulin heavy chain constant region).In certain instances, the framework includes a fragment crystallizable(Fc) region.

“Antigen-determining region” means a portion of a binding moiety thatsubstantially varies within a particular type or group of bindingmoieties. The identification of antigen-determining regions, in someinstances referred to as variable domains, is well known in the art.Exemplary antigen-determining regions include, for example, a heavychain variable domain (VH), a light chain variable domain (VL), and acomplementarity determining region (CDR; e.g., a CDR located within a VHor VL domain).

As used herein, the “type” of a polypeptide (e.g., a binding moiety)means a group of polypeptides (e.g., binding moieties) characterized bythe particular configuration of constituent regions, optionallyincluding one or more functional domains, constant regions, one or moreantigen-determining regions, one or more linkers, and/or other optionalbinding moiety cassettes known in the art. Types of polypeptides, suchas binding moieties, are known to those of skill in the art and include,without limitation, IgG (e.g., IgG1, IgG2, IgG3, and IgG4), IgM, IgA(e.g., IgA1, IgA2, and IgAsec), IgD, IgE, Fab, Fab′, Fab′2, F(ab′)2, Fd,Fv, Feb, scFv, or SMIP binding moieties. In some embodiments, apolypeptide is an scFv.

“Conversion” of a first polypeptide to a chimeric polypeptide means thatthe first polypeptide, or one or more portions thereof, is fused to asecond polypeptide, or one or more portions thereof, thereby forming achimeric polypeptide including at least a portion of the firstpolypeptide and at least a portion of the second polypeptide. In someinstances, polynucleotide segments encoding an antigen-determiningregion of a binding moiety, or fragments thereof, are combined with apolynucleotide segment encoding at least a portion of the framework of adistinct binding moiety to form a polynucleotide segment encoding achimeric binding moiety (e.g., a binding moiety of a different type).For example, the methods of the invention can be used to convert an scFvbinding moiety to, e.g., an IgG binding moiety.

“Recombination motif” means a nucleic acid sequence or domain having afirst pattern of nucleic acids that is capable of participating in arecombination event with a second nucleic acid sequence or domain havinga second pattern of nucleic acids. Two recombination motifsrecombination motifs capable of participating in a recombinationreaction with each other may be referred to as, e.g., complementary. Tworecombination motifs recombination motifs incapable of participating ina recombination reaction with each other may be referred to as, e.g.,orthogonal. The recombination reaction may involve additional reagentsor specific conditions. “Recombination enzyme” or “recombinase enzyme”means an enzyme or plurality of enzymes capable of facilitatingrecombination between complementary recombination motifs.

“Site-specific recombination motif” means a recombination motif capableof participating in a recombination event with a second recombinationmotif in a sequence-dependent manner. The site-specific recombinationevent may involve additional reagents or specific conditions. A “crypticsite-specific recombination motif” is a site-specific recombinationmotif that is hidden until a particular event (e.g., recombinationaccording the methods described herein or digestion by a restrictionenzyme) occurs. For example, a cryptic site-specific recombination motifmay be made up of two or more separate nucleic acid elements that arebrought together after recombination of two vectors according to themethods of the invention, such that upon recombination, a complete andunbroken site-specific recombination motif capable of being recognizedby a recombinase enzyme is formed. In some instances, a crypticsite-specific recombination motif can be converted into a functionalsite-specific recombination motif by a restriction digestion, such aswell known in the art.

An “ADAR enzyme” is a double-stranded RNA-specific adenosine deaminaseenzyme capable of modifying a polynucleotide at specific nucleic acids(e.g., mRNA). In some instances, an ADAR enzyme performspost-transcriptional modification, or “editing,” of an mRNA sequence,for example, by converting an adenosine to inosine. As inosine mimicsthe activity of a guanosine (e.g., pairing with cytosine), this caneffectively result in the formation of a single-nucleotide polymorphismin the transcribed mRNA sequence. In some instances, editing can resultin the formation a “cryptic” splice site, recombination motif, or othernucleic acid element. ADAR enzymes and RNA editing are described inSavva et al. (Genome Biol. 13: 252, 2012), Nishikura (Annu. Rev.Biochem. 79: 2.1-2.29, 2010), and Schoft et al. (Nuc. Acids Res. 35(11):3723-3732, 2007), each of which is incorporated herein in its entirety.

“Express” or “expression” means the transcription, or transcription andtranslation, of a polynucleotide segment. A polynucleotide segment thatis expressed is a polynucleotide segment from which a transcript hasbeen generated and, optionally, that a protein has been generated fromthe transcript. Accordingly, a transcript or protein that has beenexpressed is a transcript or protein generated by the transcription, ortranscription and translation, respectively, of a polynucleotidesegment. Two proteins, polypeptides, or polynucleotide segments that maybe expressed as a single transcript and/or protein or polypeptide may bereferred to as “fused.”

“Regulatory element” means a polynucleotide segment that contributes tothe control of the expression of a polynucleotide segment present in thesame nucleic acid, such as an adjacent and/or 3′ polynucleotide segment,or the sequence thereof. A regulatory element may, for example, increaseor decrease the expression of the polynucleotide segment. A regulatoryelement may be activated or inhibited by the binding of one or moretranscription factors. Exemplary regulatory elements include, withoutlimitation, promoters, enhancers, and silencers.

The term “vector,” as used herein, refers to any polynucleotide moleculethat can be used to carry genetic material, for example, into a cell, asknown in the art. In some instances, a vector is an expression vectorincluding one or more polynucleotides (e.g., polynucleotides encodingpolypeptides) to be expressed. Exemplary vectors include, withoutlimitation, plasmids, phagemids, cosmids, viral vectors, and artificialchromosomes (e.g., bacterial artificial chromosomes or yeast artificialchromosomes). Viral vectors may include, for example, retroviralvectors, lentiviral vectors, and adenoviral vectors. Methods forproducing such vectors are well known in the art.

By “Mitotrap protein” is meant a knocksideways bait protein including amitochondrial outer membrane targeting signal derived from the yeastprotein Tom70, a YFP reporter, an HA tag, and an FRB domain, asdescribed, for example, by Robinson and Hirst, supra. The Mitotrapprotein and other knocksideways bait proteins as contemplated herein andas known in the art, or portions thereof, may be useable firstpolypeptides, second polypeptides, or chimeric polypeptides of theinvention.

A “cryptic splice site” is an mRNA splice site that is hidden until aparticular event (e.g., recombination between a first vector and asecond vector according the methods described herein) occurs. Forexample, a cryptic splice site may be made up of two or more separatenucleic acid elements that are brought together after recombination oftwo vectors according to the methods of the invention, such that uponrecombination, a complete and unbroken mRNA splice site is present in apolynucleotide in the resultant integrant vector. As a result, when thepolynucleotide is transcribed, e.g., in a eukaryotic cell capable ofperforming mRNA splicing, the polynucleotide will be spliced at thesplice site generated by the recombination event.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing transduction of an E. coli cell with aphagemid vector. The E. coli cell includes an acceptor vector that canbe recombined with the phagemid vector, for example, by a recombinaseenzyme (e.g., phiC31). In this example, the phagemid vector encodes anscFv, in which the linker is encoded by a site-specific recombinationmotif (e.g., an attP or attB site; preferably an attP site), and theacceptor vector includes a heavy chain constant region and achloramphenicol resistance cassette.

FIGS. 2A-2C are a series of schematics showing a multifunctional intronincluding a promoter and signal peptide designed for multiple expressionhosts. (A) An artificially-constructed DNA sequence is shown, whichincludes, e.g., a CMV promoter (nucleic acid sequence shown), mammalianand bacterial signal peptides (amino acid sequence and nucleic acidsequence shown), the first portion of a VH sequence, and sequences formiscellaneous elements. (B) In this panel, the elements of the bacterialexpression cassette, which includes an E. coli lac promoter, thebacterial signal peptide, and the VH gene, are highlighted. (C) In thispanel, the elements of the mammalian expression cassette, which includesthe CMV promoter, mammalian signal peptide, the intron containing thebacterial elements (which may be excised during mRNA processing), andthe VH gene, are highlighted.

FIG. 3 is a schematic showing phiC31-mediated integration of a smallvector containing an attP site into a larger host vector containing anattB site. The positions at which the two vectors recombine form attLand attR sites upon integration.

FIGS. 4A-4C are a series of schematics showing (A) a first vector and asecond vector, (B) recombination between the first vector and the secondvector, and (C) the recombinant product of recombination between thefirst vector and the second vector, which encodes an immunoglobulinchimeric polypeptide.

FIG. 5 is a schematic showing the sequence of a multifunctional promoter(top) and protein blots showing expression of a CAM resistance protein,from the multifunctional promoter (bottom) in a number of vectors andcell types. Lanes 1-9 are Coomassie stained. E. coli lane 1 showsexpression of a protein from the multifunctional promoter in pSK215vector in E. coli. E. coli lane 2 shows expression of a protein from themultifunctional promoter in pSK215cat vector in E. coli. E. coli lane 3shows expression of a protein from the multifunctional promoter inpRSETcat vector in E. coli. E. coli lane 4 contains a molecular weightmarker. Insect lane 5 shows expression of a protein from themultifunctional promoter in pSK215cat (bacmid) in insect T. ni cells.Insect lane 6 shows expression of a protein from the multifunctionalpromoter in pFastBacCat (bacmid) in insect T. ni cells. Insect lane 7shows uninfected T. ni cells. Insect lane 8 shows T. ni cells infectedwith wild type baculovirus. Insect lane 9 contains a molecular weightmarker. Mammalian lanes 1 to 3 show Western analysis of mammalian cellline expression of cat using an anti-Cat antibody. Mammalian late 1shows Western analysis of untreated CV-1 cells. Mammalian lane 2 showsWestern analysis of CV-1 cells transfected with pSK215cat. Lane 3contains a molecular weight marker. Arrow indicates the cat geneproduct. The upper band is an artifact that is also observed in Westernanalysis of untreated cells.

FIG. 6 is a schematic showing a first polynucleotide including asite-specific recombination motif, a second polynucleotide (pATTB)including a site-specific recombination motif complementary to that ofthe pATTP construct, and a recombinant product resulting fromrecombination between pATTP and pATTB.

FIG. 7 is a schematic showing the structure of a phagemid vector(pAXM688), which contains VL, VH, CH (including an Fc region), and gpIIIgenes, as well as mammalian and bacterial controlling elements. Thephagemid vector also includes suppressible and non-suppressible stopcodons, which permit the expression of an scFv-gpIII fusion protein insuppressing E. coli strains (E. coli Sup+) and the expression of justthe scFv in non-suppressing E. coli strains (E. coli Sup−).

FIG. 8 is a schematic showing recombination between the phagemid vectorpAXM688 and an acceptor vector (pAcceptor), mediated by a phiC31integrase enzyme. Recombination results in the formation of an integrantvector including all elements of the phagemid and the acceptor vectors,except that the attB and attP sites are replaced by attL and attR sites.

FIGS. 9A-9B are schematics showing mammalian expression of an IgG in anintegrant vector produced, for example, by the integration scheme shownin FIG. 8. (A) The integrant vector includes a light chain gene and aheavy chain gene. The attL and attR site-specific recombination sites,the bacterial promoter (P_(E.c.)), and the gpIII gene are locatedbetween splice sites. (B) Thus, the pre-mRNA molecules produced bytranscription of the light chain gene or heavy chain gene may have theseelements spliced out, yielding mature mRNA molecules including only therespective mammalian signal peptides, variable and constant domains, andpolyA tails.

FIG. 10 is a schematic showing the pMINERVA system for scFv-to-IgGconversion. This system includes two vectors, a phagemid vector and anacceptor vector (pAcceptor), which can be recombined by phiC31 integraseto form an integrant vector, pMINERVA.

FIGS. 11A-11B are schematics and diagrams demonstrating that thepMINERVA system can be used to generate functional scFvs and IgGs. (A)The pMINERVA integrant vector includes a heavy chain expression cassetteand a light chain expression cassette. (B) CHO cells transfected withthe pMINERVA integrant vector can express IgG protein, while E. colicells transfected with the phagemid vector express scFv protein. Of thephiC31 integrase site-specific recombination motifs, attP, but not attB,was successfully used as a VH-VL linker to produce a functional scFv.Both attL and attR motifs were shown to be suitable as CL-VL linkers toproduce functional IgGs.

FIGS. 12A-12C are graphs and schematics showing that certain phiC31integrase site-specific recombination motifs are suitable for use aslinkers in scFvs or IgGs. (A) The same scFv with three different linkersequences (wild-type; WT (Gly4Ser)3, the phiC31 attB site, or the phiC31attP site in reading frame 2) was produced. Each scFv was tested in anELISA against the target protein or a non-relevant control.Anti-FLAG-HRP was used to detect a FLAG tag on the scFv and the ELISAwas developed with Ultra TMB reagent. The scFv with the attP linkerretained functionality relative to the standard linker. The attP motifwas successfully used as a linker in a functional scFv showing bindingactivity, but use of the attB motif as a linker resulted in an scFvshowing no binding activity. (B) The same IgG with no linker between VLand CL (WT), or the recombined phiC31 integrase sites (attL or attR) inreading frame 2, was produced. Each IgG was tested in an ELISA againstthe target protein or a non-specific control. Anti-mouse-HRP was used todetect the IgGs, and the ELISA was developed with Ultra TMB reagent. Allthree IgG constructs were expressed and functional. Each of the attL andattR motifs was successfully used as an IgG linker in a functional IgGmolecule. (C) The attL and attR motifs were tested as CL-VL linkers inthe light chain of the IgG.

FIG. 13 is a diagram showing the relative positioning of an attB site,ribosome binding site (RBS) and spacer, and chloramphenicol-resistancegene (CAM) in an exemplary donor phagemid vector. In this donor vector,the attB site for phiC31 integrase precedes (e.g., is located 5′ to) theRBS, fMet, and CAM gene. The initiating methionine (fMet) for the CAMgene is boxed. There is no promoter preceding this cassette, so cellscontaining the donor vector are CAM-sensitive.

FIG. 14 is a diagram showing the relative position of a CAM promoter,attP site, and phiC31 gene in an exemplary acceptor vector. In thisacceptor vector, the attP site is located downstream (e.g., 3′ to) ofthe promoter and upstream (e.g., 5′ to) of the phiC31 gene. Theinitiating methionine (fMet) for the phiC31 gene is boxed. This cassettelacks the CAM gene, so cells containing the acceptor vector areCAM-sensitive.

FIG. 15 is a diagram showing the integrant vector produced byrecombination of the donor vector of FIG. 13 and the acceptor vector ofFIG. 14, e.g., by a phiC31 recombinase. In this integrant vector, therecombined elements are arranged in the following order: CAM promoter,attR site, ribosome binding site (RBS), and CAM gene. In other words,the recombined phiC31 site (attR) is located downstream (e.g., 3′ to) ofthe CAM promoter and upstream (e.g., 5′ to) of the RBS, initiatingmethionine (fMet; indicated by a box) of the CAM gene, and the CAM gene.Furthermore, because the integrant vector includes a CAM promoterupstream of the CAM gene, cells containing this vector (e.g., cells thathave undergone recombination of the donor vector and acceptor vector)are CAM-resistant.

FIG. 16 is a diagram showing splicing of a synthetic intron containinggpIII introduced at the VH-CH junction of a polynucleotide encoding anIgG. The resultant vector, or a wild-type (WT) control, was transfectedinto HEK-293 cells and IgG was harvested and analyzed by SDS-PAGE. BSAstandards are shown in the three lanes between the ladder and Lanes 1-4.Lanes 1 and 2 show protein expression from the wild-type vector, whilelanes 3 and 4 show protein expression from the vector including thegpIII intron. Lanes 1 and 3 show non-reducing conditions and lanes 2 and4 show reducing conditions.

FIG. 17 is a diagram showing a means for converting an scFv to multipleIgGs and/or chimeric antigen receptors (CARs). In some instances, thisconversion may occur in a short time frame (e.g., over about one night).This scheme may be used to produce both IgGs and CAR-Ts from the samevector system by use of orthologous integrases. In this scheme, aphagemid is recombined with two distinct acceptor vectors using twodistinct integrases (phiC31 and BxB1). The phiC31 reaction results information of an integrant vector encoding an IgG (e.g., a vectorsuitable for expressing an IgG in a mammalian cell, such as a CHO cell),while the BxB1 reaction results in the formation of an integrant vectorencoding a CAR (e.g., a CAR suitable for use in a T cell assay).

FIGS. 18A-18B are diagrams showing (A) a final vector for CARexpression, and (B) a final vector for IgG expression. (A) Mammaliansplice sites (5′ ss and 3′ ss) flank the bacterial expression elementsupstream of the scFv. Another intron contains the M13 gp3 gene andrecombined BxB1 attachment site (attR). Proper splicing in mammaliancells removes the bacterial expression elements and fuses the scFv tothe hinge, transmembrane, and signaling domains of the TCRζ. A HEK-293packaging cell line can be used to produce lentivirus from this vector,and Jurkat cells can be subsequently transduced with the virus.Transduced cells express the CAR fusion and EGFP. (B) Mammalian splicesites (5′ ss and 3′ ss) flank the bacterial expression elements upstreamof the heavy chain. Another intron contains the M13 gp3 gene, BxB1attachment site (attP), and zeocin gene. Proper splicing in mammaliancells removes the bacterial expression elements upstream of the heavychain and fuses the light chain variable domain (VL) to the kappa lightchain constant domain (C_(L)). CHO cells can be transfected with thisvector to produce full length IgGs.

FIGS. 19A-19B are a series of diagrams showing phiC31-mediatedrecombination of a donor vector and an acceptor vector. (A) The pDonorand pAcceptor plasmids were co-transformed into E. coli expressingphiC31 integrase. phiC-mediated recombination between the attP and attBsites resulted in fusion of a promoter to the chloramphenicol resistancegene. Recombinants could be screened by PCR using a forward primerderived from the donor plasmid and a reverse primer derived from theacceptor plasmid. (B) A 900 bp PCR product was generated byphiC31-mediated recombination in E. coli. No product was detected whenthe two independent plasmids were mixed and used in the PCR reaction(−phiC31).

FIGS. 20A-20B are a series of diagrams showing a version of the pMINERVAvector system designed to recombine with any of at least three distinctacceptor vectors. FIG. 22A shows integration between the pMINERVAphagemid vector and an exemplary acceptor vector, pAcceptor, aftertransduction of pMINERVA into a phiC31+E. coli strain containingpAcceptor. FIG. 22B shows possible integration reactions betweenpMINERVA and three exemplary acceptor vectors (pAcceptor1, pAcceptor2,and pAcceptor3). Recombination of pMINERVA with pAcceptor1 results in a3′ fusion of the scFv to CAR elements, thereby yielding an integrantvector capable of expressing a CAR including the scFv as anextracellular binding domain. Recombination of pMINERVA with pAcceptor2results in linker exchange, in which the VH domain of the scFv is fusedto a CH domain on pAcceptor2. Recombination of pMINERVA with pAcceptor3results in a 5′ fusion of the scFv, e.g., for switching to an alternatepromoter. P_(mam), mammalian promoter; P_(yeast), yeast promoter;P_(cmv), CMV promoter; 5′ss and 3′ss, splice signals; VL, variablesection of the light chain; VH, variable section of the heavy chain;gp3, phage M13 gene3 product; P_(E. coli) , E. coli promoter; CH or Fc,constant region of the heavy chain; attB, attP, substrates for anintegrase gene; attR and attL, products of an integrase gene; polyA,polyadenylation sequence; Cam^(S), CamR, chloramphenicol resistance genewithout and with a promoter, respectively; TCRzeta, T-cell receptorzeta; CAR-T, chimeric antigen receptor; Pro^(splice), Pro^(cat),dual-function promoter-types (see text for details); IRES, internalribosome entry site; RBS, ribosome binding site.

FIGS. 21A-210 are a series of diagrams showing an scFv to IgGreformatting approach based on dual expression promoter systems: (A, C)promoter splicing (Pro^(splice)) or (B, D) catenated polyfunctionalpromoter (Pro^(cat)). (A) In the Pro^(splice) spliced promoter system, abacterial promoter (e.g., LacPO) is positioned within a mammalianintron, such that the bacterial promoter will be used to drivetranscription in a bacterial cell, but will be spliced out in a cellcapable of splicing, such as a mammalian cell. (B) In the Pro^(cat)catenated promoter system, multiple promoters (e.g., a CMV promoter,polyhedron promoter, and LacPO promoter) are concatenated to each otherupstream of the gene to be expressed. ATG start codons are removed fromthe promoters downstream of the 5′-most promoter, such that the startsite is identical for all cell types (e.g., mammalian, insect, andbacterial cells, respectively). (C) In one embodiment of a Pro^(splice)dual function promoter system, the LacPO and bacterial signal peptide(SigPep^(E.c.)) sequence may be contained within the mammalian intron.The bacterial signal peptide sequence may, for example, overlap the 3′splice site (3′ss). In E. coli, transcription from the bacterialpromoter within the mammalian intron results in the expression of thescFv in the bacterial periplasm fused to the M13gp3 protein in anamber-suppressing strain of E. coli (e.g., TG1). In mammalian cells,intron splicing of the mRNA at the 5′ (5′ss) and 3′ss removes thebacterial LacPO regulatory sequences located within the intron. Intronsplicing may desirably generate the mammalian signal sequence. Thisintron nucleotide sequence may include promoter consensus sequences,signal sequence consensus sequences, and splice site consensus sequencessuch as those known in the art. (D) In another example of a catenatedpromoter system, the ATG start sites downstream of a mammalian promoter(e.g., PCMV) may be removed from a lac promoter/operator (LacPO)controlling element. A downstream polyhedron promoter may be included asdescribed herein. The Kozak sequence and E. coli ribosomal binding site(RBS) may be designed such that the first ATG Net start site forbacterial, insect, and/or mammalian expression is identical. In oneexample, the same signal sequence (SigPep) may be used for all threeorganisms.

FIGS. 22A-22B are a series of images showing the results of splicing ofa gp3 gene in the expression of a light chain in mammalian cell cultureand expression of dual expression promoters. (A) Comparison of awild-type light chain with a light chain incorporating a gp3-splicegene. The arrow indicates the band corresponding to the light chain geneproduct. (B) Expression comparison of an IgG grown in HEK293 cells underthe expression control of either an E1A promoter, Pro^(splice) orPro^(cat).

FIG. 23 is a table showing different types of potential pMINERVAconstant framework libraries. Exemplary framework regions useful in thevector systems of the invention include, without limitation, IgY(avian), camelid, IgNAR (shark), mammalian IgG (e.g., bovine, rabbit),other IgGs, mammalian IgM, and Fab (e.g., yeast display Fab). Potentialadvantages for such frameworks, in the context of a pMINERVA library,are also provided.

FIGS. 24A-24E are a series a diagrams showing the pMINERVA transformersystem and the expression and function of scFvs and IgGs includingphiC31 integrase sites. (A) The pMINERVA system features three vectors:a pDonor phagemid vector encoding an scFv, a pAcceptor vector, and anIgG expression vector. scFv antibodies encoded on the pDonor vector asM13gpIII-fusions can be screened in a phage display biopanning procedureto identify a phagemid encoding a scFv with the desired biophysicalproperties. This phagemid is transduced into an E. coli strainexpressing phiC31 integrase and harboring an IgG acceptor vector. Therecombination event fuses the VH region to the CH region. Furthermore,the recombination event introduces both a mammalian promoter andfunctional protein initiation site 5′ to the V_(L) gene. Of specialnote, the linker between the V_(H) and V_(L) domains of the scFv iscomposed of a phiC31 36-bp attP site that is able to function as both:(i) a peptide linker between the heavy and light variable domains, and(ii) a 36-bp functional substrate for phiC31 integrase. P_(mam),mammalian promoter; 5′ss and 3′ss, splice signals; V_(L), variablesection of the light chain; V_(H), variable section of the heavy chain;gp3, phage M13 gene3 product; P_(E. coli) , E. coli promoter; C_(H) orF_(c), constant region of the heavy chain; attB, attP, substrates for anintegrase gene; attR and attL, products of an integrase gene; polyA,polyadenylation sequence; Cam^(s), CamR, chloramphenicol resistance genewithout and with a promoter, respectively; Pro^(splice), Pro^(cat),dual-function promoter-types; RBS, ribosome binding site. (B) The samescFv with two different linker sequences, WT (Gly₄Ser)₃ or the phiC31attP site in reading frame 2, was produced. Both phage-scFvs were testedin an ELISA against the purified target protein or a non-relevantantigen control. Anti-M13 antibody that is conjugated to Horseradishperoxidase (HRP) was used for phage detection and the enzyme linkedimmunosorbent assay (ELISA) was developed with UltraTetramethylbenzidine (TMB) reagent. The fold over background (FOB),which is the signal against target over the signal against non-relevantcontrol, is shown for each phage tested. Error bars represent thestandard deviation of phage binding tested in triplicate. (C) IgGmolecule modeled with attL and attR. The attL (thick blue loop) and attR(thick red loop) peptides are inserted schematically in a typical humanIgG1 molecule (PDB ID: 1hzh) shown as ribbons (heavy chain: white, lightchain: cyan). (D) The same IgG, with either no linker or the recombinedphiC31 integrase attL site between the IL2 signal sequence (ss) andV_(L), was produced. In parallel, expression of the wild-type IgG wascompared to expression of the same IgG with the recombined phiC31integrase site attR site between V_(H) and C_(H). A coommassie stainedSDS-PAGE gel is shown. (E) An IgG with attL between the IL2ss and theV_(L) (top graph) and an IgG with attR between V_(H) and C_(H) (bottomgraph) were tested for binding to both a specific and a non-relevanttarget antigen in a cell ELISA. The binding of both molecules wascompared to the binding of a wildtype IgG. Both ELISAs usedanti-human-HRP to detect the IgGs and the ELISA was developed with UltraTMB reagent. The ODs at 450 nm are shown.

FIGS. 25A-25J are a series of diagrams and tables showing use andvalidation of the pMINERVA system and permutations thereof. (A) Positiveselection of phiC31 integrase activity. The two plasmids of the pMINERVAsystem, pDonor and pAcceptor, each having a needed component in transfor a functional camR gene, were constructed. The attP site (underlined)in pDonor was flanked upstream by the E. coli 5′ controlling elementsand. The attB site (lower case DNA sequence) in pAcceptor was placed 5′of the promoter-less camR gene. Successful recombination between theattP and attB sites on the two plasmids in the presence of the phiC31integrase (blue dashed line) generates the co-integrant (pMINERVA;bottom sequence) and fuses an E. coli promoter in front of thebi-cistronic heavy chain-CamR message. (B) Expression and function ofscFvs and IgG containing splice sites flanking the M13 gpIII gene.Competent TG1 cells containing pAcceptor were transformed with pDonor ora control mock-recombined vector and grown on plates containingampicillin or chloramphenicol. The ratio of colonies on the ampicillinplates to the chloramphenicol plates was calculated. (C) Phage-scFvfusions with and without splice sites flanking the M13 gpIII gene inpDonor were produced from E. coli and tested for functionality in aphage ELISA. The phage-scFv were tested for binding to purified targetantigen and a non-relevant control protein. The fold over background(FOB) is shown for both. Error bars represent the standard deviation ofphage binding, tested in triplicate. (D) The same IgG, with either nolinker or the intron containing the M13 gpIII gene between the V_(H) andC_(H) was produced. An ochre stop codon placed 3′ of the M13 gpIII geneprevents full length light chain protein expression from non-splicedmRNAs. The upper arrow indicates the band corresponding to the heavychain and the lower arrow corresponds to the light chain gene product inthe SDS-PAGE. IgG molecules were tested for functionality in an ELISAusing purified antigen. FOB (fold-over-background) signal is shown forboth. (E) In the catenated dual promoter system (Pro^(cat)), the ATGsdownstream of the mammalian EF1a promoter (P^(EF1a)) are removed fromthe downstream polyhedron (not shown) and PhoA bacterial promoter. TheKozak sequence and E. coli ribosomal binding site (RBS) are designedsuch that the first ATG Net start site for either bacterial, insect (notshown) or mammalian expression is identical. In this case, the samesignal sequence (SigPep) is used for all three organisms. (F) In thespliced dual function promoter system (Pro^(splice)), the LacPO andbacterial signal peptide (SigPep^(E.c.)) sequence are contained withinthe mammalian intron. The bacterial signal peptide sequence overlaps the3′ splice site (3′ss). In E. coli, transcription from the bacterialpromoter within the mammalian intron results in the expression of thescFv in the bacterial periplasm fused to the M13 gpIII protein in anamber-suppressing strain of E. coli (for example, TG1). In mammaliancells, intron splicing of the mRNA at the 5′ (5′ss) and 3′ss removes thebacterial LacPO regulatory sequences located within the intron. Intronsplicing generates the mammalian signal sequence. (G) Phage-scFvproduction from the Pro^(cat) and Pro^(splice) promoters. Phage weretested for binding to purified target antigen and to a non-relevantcontrol antigen in a phage ELISA. FOB (fold-over-background) signal isshown and error bars represent the standard deviation of phage bindingtested in triplicate. (H) Expression of the wild type (wt), Pro^(splice)and Pro^(cat) promoters in HEK293 mammalian cells. IgG purification fromHEK293 cells where the IgG heavy chain gene was under the expressioncontrol of either an EF1A promoter alone, Pro^(splice) or Pro^(cat). (I)Genetic elements used in the pDonor and pAcceptor system. The source ofeach element used in the pMINERVA system is indicated. Also indicated iswhether the genetic element was synthesized or cloned from an existingplasmid. (J) Yield analysis of IgG expression test vector. Eleven scFvV_(H) and V_(L) sequences were cloned into a single IgG expression testvector using the Pro^(cat) promoter to drive the heavy chain. The IgGvectors were transfected into HEK293 cells and the secreted IgG proteinswere purified from the supernatant six days post-transfection. Theamount of final purified IgG was determined and yields were calculatedbased on transfecting 100 mL cell culture volumes.

FIGS. 26A-26E are a series of diagrams showing expression and splicingin the pMINERVA system, including expression promoter systems andco-integrant expression yield. (A) Promoter type Pro^(splice). In thisdual function promoter, the LacPO and bacterial signal peptide(SigPep^(E.c.)) sequence are contained within the mammalian intron. Thebacterial signal peptide sequence overlaps the 3′ splice site (3′ss). InE. coli, transcription from the bacterial promoter within the mammalianintron results in the expression of the scFv in the bacterial periplasmfused to the M13gp3 protein in an amber-suppressing strain of E. coli(for example, TG1). In mammalian cells, intron splicing of the mRNA atthe 5′ (5′ss) and 3′ss removes the bacterial LacPO regulatory sequenceslocated within the intron. Intron splicing generates the mammaliansignal sequence. The intron nucleotide sequence was designed usingpromoter consensus sequences, signal sequence consensus sequences, andsplice site consensus sequences. (B) Promoter type Pro^(cat). In thiscatenated promoter system, the ATGs downstream of the mammalian CMVpromoter (P_(CMV)) are removed from downstream polyhedron and lacpromoter/operator (LacPO) controlling elements. The Kozak sequence andE. coli ribosomal binding site (RBS) are designed such that the firstATG fMet start site for either bacterial, insect, or mammalianexpression is identical. In this case, the same signal sequence (SigPep)is used for all three organisms. (C) Expression of the wild type (WT),Pro^(splice) and Pro^(cat) promoters in HEK293 cell culture. IgGpurification from HEK293 cells where the IgG gene was under theexpression control of either an EF1A promoter, Pro^(splice), orPro^(cat). (D) Light-chain gp3 splicing M13gp3 intron splicing inPro^(splice). A wild-type light chain protein was compared with a lightchain protein incorporating a spliced M13gp3-splice gene. An ochre stopcodon in pMINERVA placed 3′ of the M13gp3 gene prevented full lengthlight chain protein expression from non-spliced mRNAs. Arrow indicatesthe band corresponding to the light chain gene product. (E) Comparisonof single-plasmid and co-integrant IgG yields from HEK293 cells.Estimated yields for co-integrants estimated by gel imaging (fromSDS-PAGE): 1. pAX1984=19.4ug/mL (wild-type IgG), 2. pAX3A-5=11.6 ug/mL(co-integrant), 3. pAX3B-5=13.5 ug/mL (co-integrant).

FIG. 27 is a diagram showing a pMINERVA scheme for in vivo overnightsubcloning of an scFv into an IgG. All subcloning steps are performed byintron splicing and integrase recombination.

FIGS. 28A-28B are a series of diagrams showing examples of 3′ fusionconstructs that may be used, for example, in pAcceptor plasmids of theinvention, and an exemplary pAcceptor vector expressing an scFv that maybe converted to a pMINERVA integrant vector expressing an IgG.

FIG. 29 is a diagram showing co-integration of each of a set ofpAcceptor vectors with a pDonor vector encoding the VH, VL, and CLdomains of a human anti-Her2 antibody. h_(CH(control))=human IgG1 CHcontrol; hC_(H)=human IgG1 CH; rC_(H)=rabbit CH; and rC_(H-FLAG)=rabbitCH with modified FLAG tag. Proper co-integration and sequence wasconfirmed for each of the resultant integrant vectors.

FIGS. 30A-30B are a series of diagrams showing expression of hybridchimera IgGs under non-reducing (A) and reducing (B) conditions.

FIGS. 31A-31C are a series of graphs showing functional validation ofhybrid chimeras. H-H=human-human; H-R=human-rabbit chimera.

FIG. 32 is a graph showing functional validation of a hybrid chimera.The FLAG tag in the hybrid chimera was confirmed to be functional.

DETAILED DESCRIPTION

In general, the present invention provides methods and compositions forconverting a first polypeptide into a chimeric polypeptide. In someembodiments, the invention includes at least two vectors: a first vectorincluding the sequence of the first polypeptide and a second vectorincluding the sequence of a second polypeptide. The vectors includecomplementary site-specific recombination motifs such that site-specificrecombination between the two vectors results in the generation of achimeric polypeptide including at least a portion of the firstpolypeptide and at least a portion of the second polypeptide. Asite-specific recombination motif may be positioned within an intron orwithin a coding sequence on the first or second vector.

Methods of Converting a First Polypeptide into a Chimeric Polypeptide

The present invention provides methods for converting a firstpolypeptide into a chimeric polypeptide using, for example, a pair ofvectors that can be recombined. For example, one of the vectors includesa polynucleotide segment encoding the first polypeptide, or a fragmentthereof, while the second vector includes a polynucleotide segmentencoding the second polypeptide, or a fragment thereof. Each of thevectors further includes a recombination motif (e.g., a site-specificrecombination motif), such that the two vectors can be integrated by arecombinase enzyme, such as an integrase (e.g., phiC31 integrase). Thus,the methods of the invention involve providing the pair of vectors andinducing recombination, thereby integrating the two vectors into anintegrant vector in which the first polypeptide, or a fragment thereof,and the second polypeptide, or a fragment thereof, are fused to form thechimeric polypeptide. Vectors, recombinase enzymes, and recombinationmotifs that may be used in the methods of the invention are described indetail below.

In some instances, the recombination event occurs in a cell. Forexample, a cell may contain both vectors and the recombinase enzyme,thereby initiating integration of the vectors. In certain embodiments,the cell initially contains one vector (e.g., the second vector) and istransfected or transformed with the other vector. A gene encoding therecombinase enzyme may be present in one of the first or second vectors,a third vector within the cell, or in the genome of the cell. Avariation of this method is contemplated in which the polynucleotideencoding a first polypeptide or a second polypeptide can be present inthe genome of the cell, rather than in a vector. The genomic sequencemay be positioned near to or contain a recombination motif that can berecombined with the recombination motif of a first vector or a secondvector of the invention. As such, recombination between therecombination motif of the vector and the genomic recombination motifresults in integration of elements of the vector (e.g., a polynucleotidesequence encoding a first polypeptide or a second polypeptide, or afragment thereof) into the genome of the cell.

In some instances, the recombination event occurs in vitro. For example,the first and second vector may be present in a solution together with arecombinase enzyme (e.g., bacteriophage lambda integrase). In certaininstances, the first vector, second vector, and a recombinase enzyme maybe present in a container, such as an emulsion droplet. Distinctcombinations of first vectors, second vectors, and/or recombinaseenzymes can be present in each of a plurality of emulsion droplets. Assuch, a plurality of distinct integrant vectors can be generated in aseries of parallel reactions, each occurring in a separate emulsiondroplet. Emulsion droplets may thus be used for, e.g., immunorepertoirecloning.

For example, a plurality of polypeptides (e.g., polypeptides eachincluding a distinct antigen-determining region, such as variabledomains or CDRs) may each be encoded on separate first vectors. In someinstances, each first vector is contained in a separate emulsiondroplet. Each emulsion droplet may further include a second vector and arecombinase enzyme. In one embodiment, each of the second vectorsencodes the same framework. Thus, in this example, a plurality ofintegrant vectors, each including, e.g., a distinct antigen-determiningregion, but all containing the same second polypeptide, or a fragmentthereof, are produced as a result of recombination between the firstvector and the second vector present within each emulsion droplet.

Compositions

The invention features compositions including a vector encoding a firstpolypeptide that can be converted to a chimeric polypeptide (e.g., apolypeptide of a different type) according to the methods describedherein. The composition may further include a second vector encoding asecond polypeptide. The second polypeptide, or a fragment thereof, canbe combined with the first polypeptide, or a fragment thereof, to formthe chimeric polypeptide. Each of the vectors may include arecombination motif (e.g., a site-specific recombination motif). In someinstances, the site-specific recombination motif of the two vectors arecomplementary, such that a recombinase enzyme (e.g., as describedherein) can recombine the two vectors to form an integrant vectorincluding components of both of the original vectors (e.g., thepolynucleotide encoding the first polypeptide, the polynucleotideencoding the second polypeptide, or portions thereof). The compositionmay also include the recombinase enzyme. Exemplary vectors andrecombinase enzymes suitable for inclusion in compositions of theinvention are described in detail herein.

Vectors

The present invention features nucleic acid vectors (e.g., a firstvector or a second vector) that may be used to convert a firstpolypeptide into a chimeric polypeptide (e.g., a polypeptide of adifferent type). Two such nucleic acid vectors may include site-specificrecombination motifs that permit recombination between the two vectorsto produce a recombination product (e.g., an integrant vector) includingelements from the two original vectors (e.g., in the form of apolynucleotide segment encoding a chimeric polypeptide). Preferably, afirst vector includes a first polypeptide to be converted, and a secondvector includes a second polypeptide (e.g., a polypeptide including abinding moiety framework and/or a functional domain of interest). Thesecond polypeptide, or a fragment thereof, may be fused to the firstpolypeptide, or a fragment thereof, to form a chimeric polypeptide. Assuch, site-specific recombination between the first vector and thesecond vector results in the formation of an integrant vector encodingthe chimeric polypeptide.

An integrant vector of the invention may include any component of afirst vector and/or a second vector. In some instances, an integrantvector may be used as a first vector or a second vector in a furtherrecombination reaction with a further vector (e.g., a further vectorincluding a further first polypeptide or a further second polypeptide),thereby forming another integrant vector including portions of theoriginal integrant vector and the further vector. This may be used, forexample, to convert the chimeric polypeptide back into the firstpolypeptide, or to, e.g., convert the chimeric polypeptide into afurther chimeric polypeptide including at least a portion of thechimeric polypeptide and the further first polypeptide or further secondpolypeptide.

A vector of the invention (e.g., a first vector, a second vector, or anintegrant vector) may include multiple distinct site-specificrecombination motifs (e.g., orthogonal site-specific recombinationmotifs or complementary site-specific recombination motifs). Forexample, a vector may include 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or moresite-specific recombination motifs. In some instances, a vector mayinclude a mix of complementary and orthogonal site-specificrecombination motifs, such that the vector can be recombined internallyvia the complementary site-specific recombination motifs, or recombinedwith another vector containing a site-specific recombination motifcomplementary to one of the site-specification recombination motifs ofthe vector.

In some instances, a vector of the invention may be capable ofexpressing one gene (e.g., a gene encoding a first polypeptide) in onecell type, and a second gene in a second cell type. In certaininstances, a vector may be capable of expressing one variant of a gene(e.g., a gene encoding a first polypeptide) in one cell type (e.g.,expressing an scFv in bacterial cells), and a second variant of the samegene in a second cell type (e.g., an scFv-Fc fusion or an IgG inmammalian or insect cells). For example, one or more portions of onevariant of the gene may be positioned within an intron, such that theseportion(s) are expressed in cells that do not perform intron splicing,such as bacteria, but are removed from the transcript by intron splicingin eukaryotic cells (e.g., mammalian cells and insect cells). In oneexample, an antibody fragment (e.g., a Fab fragment or scFv) fused to aphage coat protein, suitable for use in phage display, can be expressedin bacteria (e.g., E. coli) while a full-length IgG variant of theantibody fragment can be expressed in mammalian cells from a singlevector by embedding the phage coat protein in an intron within theimmunoglobulin heavy chain gene (see, e.g., Tesar and Hotzel, Prot. Eng.Des. Selection 26(10): 655-662, 2013; incorporated herein by reference).

A vector may include regulatory elements (e.g., promoters, enhancers,and silencers) that control the expression of particular variants inparticular cell types. In some instances, a vector of the invention maybe able to express a gene (or variants and/or portions thereof) inmultiple cell types. For example, the vector may include a plurality ofregulatory elements, each capable of controlling (e.g., activating orinhibiting) expression of the gene in a distinct cell type. In certaininstances, one or more of these regulatory elements may be positioned inan intron, as described herein.

In some instances, a vector includes one or more site-specificrecombination motifs. Such site-specific recombination motifs may, forexample, permit excision of elements from the vector and/orsite-specific recombination with a second vector to generate a hybridvector. Site-specific recombination between two vectors may result inthe generation of an integrant vector encoding a chimeric polypeptide,as described herein. A vector of the invention (e.g., a first vector ora second vector) can be produced, for example, according to methods wellknown in the art. For example, existing expression vectors can bemodified by standard techniques, including, for example, restrictionenzyme digestion, ligation, polymerase chain reaction (PCR),site-directed mutagenesis, and random mutagenesis. Vectors can also besynthesized, for example, as described in U.S. Provisional ApplicationNo. 62/087,440, incorporated herein by reference. A library of vectors(e.g., a phage display library) can be generated according to methodsknown in the art. For example, a library can be produced by directedevolution, e.g., as described in PCT Application No. PCT/US2014/018672,incorporated herein by reference. A library of vectors (e.g., firstvectors or second vectors) may be generated, for example, as variants ofan initial clone (e.g., by mutagenesis methods well known in the art). Avector library may also be generated, for example, by the methodsdescribed in PCT Publication No. WO 2014/134166, incorporated herein byreference in its entirety.

The vectors of a vector library can be screened for antigen binding, forexample, by delayed infectivity methods (e.g., delayed emulsioninfectivity screening), such as described in PCT Application No.PCT/US2014/068595, incorporated herein by reference in its entirety, orby other screening methods known in the art (e.g., biopanning methodssuch as phage display screens). In some instances, a vector library isscreened in multiplex. scFvs identified as binding to target molecules(e.g., proteins) of interest according to such methods can then beconverted to chimeric polypeptides (e.g., IgGs and chimeric antigenreceptors) according to the methods of the present invention. In someinstances, the nucleic acid sequence of a vector of the invention (e.g.,a first vector or a second vector), or a portion thereof, can bedetermined according to sequencing methods well known in the art (e.g.,Sanger sequencing or next-generation sequencing techniques).

Particular vectors useful in the methods of the present invention aredescribed in detail below. It is appreciated that a first vector, asdescribed herein, may be used as a second vector, and a second vector,as described herein, may be used as a first vector.

The First Vector

The present invention involves, in some instances, two vectors: a firstvector encoding a first polypeptide (e.g., a binding moiety) and asecond vector encoding a second polypeptide (e.g., a binding moietyframework, or portions thereof). In some instances, the first vector isa phagemid vector (FIG. 1). In certain instances, the first polypeptideis fused to a viral protein, such as a viral coat protein (e.g., GpIII).Preferably, a phage particle expressing the first polypeptide is capableof infecting a cell, such as a bacterial cell (e.g., an E. coli cell),thereby transducing the phagemid DNA into the cell. In particularinstances, the bacterial cell contains the second vector (shown in FIG.1 as the acceptor vector) and a recombinase enzyme (e.g., phiC31), suchthat the first and second vector undergo recombination in the bacterialcell to form a vector containing a polynucleotide encoding a chimericpolypeptide (e.g., a chimeric polypeptide including at least a portionof the first polypeptide and at least a portion of the secondpolypeptide). The first polypeptide encoded by the first vector may be abinding moiety having been selected, cloned, isolated, sequenced, orotherwise generated or identified by a method of screening for, e.g.,antibodies capable of binding one or more particular antigens. Forinstance, the first polypeptide can be a binding moiety identified by abiopanning technique such as phage display, ribosome display, or PhageEmulsion, Secretion, and Capture (Phage ESCape). In some embodiments,the first polypeptide is a binding moiety generated by rational design.In various embodiments of the present invention, because biopanningoften includes expression of candidate binding moieties from a vector,the first polypeptide of the present invention is encoded by a vectorused to express the first polypeptide in a method of biopanning,examples of which include phage display, ribosome display, or PhageESCape.

The first vector encoding the first polypeptide may further encode oneor more functional cassettes (e.g., as described herein). A functionalcassette of the first vector may be any polynucleotide segment capableof contributing to the generation, expression, or isolation of achimeric polypeptide, other than the polynucleotide encoding the firstpolypeptide itself. The polynucleotide segment encoding the firstpolypeptide, or a portion thereof, may be fused to a functional cassetteencoding a second polypeptide, or a fragment thereof, such that thefirst polypeptide is expressed as a fusion protein including the firstpolypeptide and one or more additional amino acids encoded by one ormore functional cassettes. A functional cassette may encode a protein orpolypeptide expressed independently of the first polypeptide, such that,when expressed, it is transcribed as a separate transcript from anytranscript encoding the first polypeptide.

The expression of one or more polypeptides and/or functional cassettescan be driven by various regulatory cassettes, as described herein.Multiple promoter cassettes may be arranged such that the firstpolypeptide, or variants thereof, may be expressed in a plurality ofdistinct cell types, or such that cell type can determine the expressionof protein variants, each variant including at least a segment encodedby the same polynucleotide segment.

The first vector can further encode one or more signal peptidefunctional cassettes (e.g., a cassette encoding a bacterial signalpeptide or a mammalian signal peptide). In some instances, the firstvector encodes one or more signal peptides 3′ of the first polypeptide.In certain instances, the first vector encodes one or more signalpeptides 5′ of the first polypeptide. A signal peptide functionalcassette may be fused to the first polypeptide or to another functionalcassette. In particular instances, the first polypeptide encoded by thefirst vector is expressed in a fusion protein that includes one or moresignal peptides, e.g., an N terminal signal peptide.

In some embodiments of the present invention, the expression of one ormore signal peptides depends upon the cell in which the first vector ispresent. For instance, the first vector may encode each of a mammaliansignal peptide and a bacterial signal peptide 5′ of the firstpolypeptide. In some instances, the mammalian signal peptide is encoded5′ of the bacterial signal peptide, although the opposite order, e.g.,is also contemplated. The mammalian signal peptide may be expressed froma mammalian promoter, while the bacterial signal peptide may beexpressed from a bacterial promoter. In particular embodiments, thebacterial promoter and bacterial signal peptide functional cassette areproximal to the first polypeptide-encoding sequence, such thatexpression in bacteria results in a fusion protein including thebacterial signal peptide and the first polypeptide. Further, thebacterial promoter and signal peptide cassette are flanked by splicesites, such that, in mammalian cells, expression of the mammalianpromoter results in a fusion protein including the mammalian signalpeptide and the first polypeptide, but not the bacterial signal peptideor promoter. In one example of such an embodiment, the first vectorencodes, from 5′ to 3′, a mammalian promoter, a mammalian signalpeptide, a splice site, a bacterial promoter, a bacterial signalpeptide, a second splice site, and the first polypeptide. In someinstances, a polynucleotide encoding a signal peptide (e.g., a bacterialor mammalian signal peptide) is positioned within an intron, such thatit is only expressed by a prokaryotic cell (e.g., a bacterial cell), asit would be removed during intron splicing in a eukaryotic cell. In aparticular instance, a polynucleotide encoding a bacterial signalpeptide is positioned in an intron, such that it is expressed as afusion with the first polypeptide in a bacterial cell, but is splicedout in a mammalian cell.

The first polypeptide may be present in a fusion protein that includes asegment that enables display. This may be the case, e.g., if the firstvector encodes a binding moiety identified by a biopanning technique inwhich the binding moiety was displayed. In some instances, a firstpolypeptide is present in a fusion protein that further includes asegment that enables viral display. A segment that enables viral displaymay be, e.g., a polypeptide including a sequence of a known viraltransmembrane domain or a sequence derived therefrom. In particularexamples, a polypeptide (e.g., a first polypeptide) of the presentinvention is present in a fusion protein that includes GpIII (e.g., M13GpIII). The functional cassette encoding GpIII may be, e.g., 3′ of thepolynucleotide segment encoding the binding moiety. Many otherconstructs for display or other use in particular methods of biopanningare known in the art.

The first vector may further encode one or more marker proteins that,upon expression, manifest a detectable phenotype. In particularinstances, the first vector encodes two or more marker proteins, e.g.,two or more marker proteins expressed from distinct promoters. In suchinstances, it may be that one marker protein is expressed, e.g., from abacterial or mammalian promoter and another marker protein is expressed,e.g., from a second bacterial or mammalian promoter. In certaininstances, one marker protein is expressed from bacterial promoter, andanother is expressed from a mammalian promoter. In some instances, apolynucleotide encoding a marker protein is positioned within an intron,such that it is only expressed by a prokaryotic cell (e.g., a bacterialcell), as it would be removed during intron splicing in a eukaryoticcell.

The first vector may include one or more site-specific recombinationmotifs (e.g., complementary and/or orthogonal site-specificrecombination motifs). Recombination between two complementarysite-specific recombination motifs present on two separate vectors canresult in the production of a recombinant product that includes, forexample, nucleic acids of the first vector and nucleic acids of thesecond vector (e.g., a recombinant product encoding a chimericpolypeptide, in which the chimeric polypeptide includes at least aportion of a first polypeptide encoded by a first vector and at least aportion of a second polypeptide encoded by a second vector). Methods andcompositions for conversion of a first polypeptide into a chimericpolypeptide using such a first vector and a second vector are describedherein.

In other instances, a first vector may include two complementarysite-specific recombination motifs, such that recombination may occurwithin the vector between these two complementary site-specificrecombination motifs. In certain instances, recombining these twosite-specific recombination motifs within the first vector results inexcision or inversion of the nucleic acids positioned between the twocomplementary site-specific recombination motifs. Alternatively,recombination between these two site-specific recombination motifs mayresult in conversion of a first polypeptide into a chimeric polypeptide(e.g., without utilizing a second vector). In either case, the point orpoints of recombination may be marked by hybrid recombination sites,generated as the combination of a portion of the first site-specificrecombination motif and portion of the second site-specificrecombination motif. As an example, attL and attR are hybridrecombination motifs produced by recombination between a first vectorhaving an attB site-specific recombination motif and a second vectorhaving an attP site-specific recombination motif.

The first vector may include a pair of complementary site-specificrecombination motifs positioned such that, in the presence of arecombinase enzyme capable of mediating recombination between the sitespecific recombination motifs, a portion of the first vector is excised.A pair of complementary site-specific recombination motifs present inthe same vector may be referred to as an excision motif pair. Inparticular embodiments, the excision removes from the first vector oneor more functional units, such as a functional cassette encoding amarker protein. In some embodiments, the excision removes a portion of apolypeptide (e.g., a first polypeptide), such as a binding moietyconstant region. In some instances, the excision could remove a GpIII(e.g., M13 GpIII)-encoding functional cassette of a binding moietyfusion protein. The excision of a portion of the first vector may be adesirable step in achieving conversion of a first polypeptide into achimeric polypeptide according to the methods described herein.

The first vector can encode a binding moiety framework functionalcassette. In some instances, the binding moiety framework functionalcassette is separated from the polynucleotide segment encoding the firstpolypeptide by one or more other functional cassettes. In particularinstances, all or a substantial portion of the interveningpolynucleotides between the polynucleotide segment encoding the firstpolypeptide and the binding moiety framework functional cassette areflanked by the site-specific recombination sites of an excision motifpair. In such embodiments, excision results in the generation of apolynucleotide segment capable of expressing a fusion protein thatincludes all or a portion of the first polypeptide and the frameworkencoded by the binding moiety framework cassette. In some instances, abinding moiety framework cassette of the first binding moiety may encodea framework corresponding to a different polypeptide type from the typeof the first polypeptide. In other instances, the binding moietyframework cassette and/or second polypeptide is of the same type but itsarrangement contributes to the conversion of the first polypeptide to apolypeptide of a different type.

The first vector may include a polynucleotide segment encoding atranscriptional stop signal, such as a polyA cassette. For example, ifthe first vector includes a binding moiety framework cassette, the polyAcassette may be 3′ of the framework cassette. Eukaryotic transcriptionalstop signals include, e.g., a polyA addition sequence (AAAUAA) and/or aplurality of downstream nucleotides. Numerous transcriptional stopsequences are known in the art and a variety of these have been used inthe expression of genes from vectors. Certain arrangements involve theinclusion of a fragment including an intron and a transcriptional stopsequence following the end of a coding sequence. Examples of intronsknown in the art include the rabbit β-globin intron and the SV40 intron.Examples of transcriptional stop sequences include those from SV40 orhuman growth hormone. Examples of combined sequences include an SV40intron/stop, the last exon of human growth hormone plus stop sequences,or the entire human growth hormone gene.

In some embodiments, the first vector includes a recombination motif(e.g., a site-specific recombination motif) capable of participating ina site-specific recombination event with the second vector of thepresent invention. Preferably, the second vector, but not the firstvector, has a site-specific recombination motif complementary to such asite-specific recombination motif of the first vector (i.e., the firstvector does not include the complement of the motif capable ofrecombining with the second vector). It is contemplated that the firstvector may include multiple, distinct, site-specific recombinationmotifs capable of recombination with the second vector, and furthercontemplated that the presence of various recombinase enzymes maymediate which, if any, of these motifs may recombine. The first vectormay further include one or more cryptic recombination motifs, eachincluding a plurality of polynucleotide segments that can be joined toform a functional recombination motif. The cryptic recombination motifmay be non-functional prior to joining of the polynucleotide segments.For example, the first vector may undergo a first recombination eventthat results in the formation of a functional recombination motif fromthe polynucleotide segments of the cryptic recombination motif.

The presence of complementary site-specific recombination motifs can beevaluated in view of the available recombinase enzymes. In certainembodiments, the first vector includes only one of each site-specificrecombination motif capable of participating in a site-specificrecombination event with the second vector. Various sets ofcomplementary recombination motifs suitable for use in the first vectorare known in the art. For example, a pair of complementary recombinationmotifs may include an attP motif and an attB motif. In a second example,a pair of complementary recombination motifs may include a hixL motifand hixR motif. Other examples of site-specific recombination motifsinclude the Tn7 site-specific attTn7 motif. Other examples are known inthe art.

In addition to the above-mentioned cassettes and other sequenceelements, the first vector of the present invention can include as anadditional functional cassette one or more stop codons. Because thevectors of the present invention, or polynucleotide segments thereof,can be expressed in multiple cell types, it is relevant that codon usageof stop codons varies across some species. For instance, the amber stopcodon (UAG) can be suppressed by certain strains of bacteria.Accordingly, it is possible to include stop codons that function incertain cell types while being read through in others, e.g., certainbacterial cell types. Exemplary stop codons that can be used selectivelyin this fashion include amber stop codons, ochre stop codons (UAA), andopal stop codons (UGA). The first vector of the present invention caninclude, e.g., an amber stop codon between the last nucleotide encodingthe first polypeptide and the first nucleotide encoding a subsequentcassette. In still more particular examples, the first vector includesan scFv binding moiety in a fusion protein including GpIII (e.g., M13GpIII), and the amber stop codon is positioned between the lastnucleotide encoding the VH or VL of the scFv and the first nucleotideencoding GpIII (e.g., M13 GpIII).

The Second Vector

The second vector of the present invention recombines with the firstvector to generate a recombination product encoding a chimericpolypeptide. In some instances, the second vector encodes a secondpolypeptide, for example, a framework (i.e., at least one constantregion) of a binding moiety, or a portion thereof. The secondpolypeptide encoded by the second vector may be a frameworkcorresponding to a type of polypeptide different from the type of thefirst polypeptide (e.g., a distinct binding moiety type). Alternatively,the framework encoded by the second polypeptide may be consistent withthe type of the first polypeptide, but positioned in a manner such thatthe rearrangement of antigen-determining and constant regions in thechimeric polypeptide nevertheless constitutes conversion. The secondpolypeptide of the second vector may be encoded by one or more frameworkcassettes. The chimeric polypeptide may be a single protein or two ormore independently expressed proteins capable of forming, for example, asingle binding moiety, such as a pair of antibody chains. Distinctsecond vectors can be used in the methods of the invention (e.g., torecombine with a particular first vector) to construct distinctrecombination products including polynucleotide segments encodingdistinct chimeric polypeptides (e.g., distinct IgG fusions, chimericantigen receptors, ubiquitin ligase fusions, and/or knocksidewaysproteins). For example, distinct second vectors each including aframework from a different species can be used to swap one or moreantigen-determining regions between binding moiety frameworks from eachspecies. In one example, a light chain and/or heavy chain variabledomain from a first vector is fused to a human framework in the secondvector to form a humanized binding moiety (e.g., a humanized IgG).

In some instances, a framework encoded by the second vector includes atleast one constant region of a binding moiety. For instance, theframework may be, be derived from, or include, e.g., an immunoglobulinconstant region, such as a CL, CH1, CH2, or CH3. In certain instances,the framework may include an entire CH domain (e.g., including CH1, CH2,and CH3). An immunoglobulin constant region may be, be derived from, orinclude a constant region associated with or derived from, e.g., a humanIg κ, Ig λ, IgA α1, IgA α2, IgD δ, IgE ε, IgG γ1, IgG γ2, IgG γ3, IgGγ4, or IgM μ chain. A framework may also be, be derived from, or includea combination of these, such as an Fc region. A framework may be, bederived from, or include one or more human T cell constant regions, suchas a TcR Cγ1 or TcR Cγ2. A framework of the present invention may bederived from a chicken, human, rabbit, goat, mouse, camel, shark, orother organism capable of producing antibodies or other binding moietiesthat include constant regions. A framework of the present invention mayalso be the framework of an artificially designed binding moiety. Aframework may be modified from any form known to be present in nature,provided that the framework is capable of functioning within a bindingmoiety construct. Many binding moiety constructs are known in the artand any of these may be utilized in whole or in part within theconstructs of the present invention. All or a portion of any of theseframeworks, or a framework derived therefrom, may be included in a firstvector or second vector framework cassette.

The second vector may further encode one or more functional cassettes inaddition to the one or more framework cassettes. A functional cassetteof the second vector may be any polynucleotide segment capable ofcontributing to the generation, expression, or isolation of a chimericpolypeptide. A functional cassette may encode a protein or polypeptide,e.g., a protein or polypeptide that is not fused to a binding moietyframework of the second vector. A functional cassette may alternativelybe a regulatory polynucleotide segment, such as a promoter, polyAsequence, Kozak sequence, or other polynucleotide segment that regulatesexpression. A functional cassette may be a polynucleotide segment thatmediates transcription or transcript stability, translation, orrecombination. A regulatory cassette can be, e.g., a promoter capable ofdriving expression of a chimeric polypeptide or a component thereof.Numerous polynucleotide sequences capable of regulating gene expressionare known in the art, as are methods for their application in directingexpression. In some instances, two or more functional cassettes may beexpressed as a fusion protein.

The expression of one or more cassettes encoding protein or polypeptidemay be driven by various regulatory cassettes. As is known in the art,various promoters are optimized for expression in a particular celltype. For instance, some promoters are only, or substantially only,capable of driving expression when present in a bacterial cell. Otherpromoters are only, or substantially only, capable of driving expressionwhen present in a mammalian cell, or in an insect cell. Some promotersare only, or substantially only, capable of driving expression in stillmore particular subsets of cell types, while others may functionalbroadly, e.g., in both a bacterial cell and a mammalian cell. Thesedifferences may result, in part, from the availability and function ofdistinct cellular proteins endogenous to the relevant cell types. Asdescribed in greater detail herein, multiple promoter cassettes may bearranged such that a single polynucleotide segment encoding a protein orpolypeptide may be expressed in a plurality of distinct cell types, orsuch that cell type can determine the expression of protein variants,each variant including at least a portion encoded by the samepolynucleotide segment.

In some instances, the second vector encodes one or more signal peptidefunctional cassettes. In some instances, the second vector encodes oneor more signal peptides 5′ of a second polypeptide cassette (e.g., aframework cassette). In certain instances, the second vector encodes oneor more signal peptides 5′ of a framework cassette. A signal peptidecassette may be optionally fused to a framework cassette or to anothercassette. In particular instances, the chimeric polypeptide or acomponent thereof is expressed in a fusion protein that includes one ormore signal peptides originating from the second vector.

The second vector may further encode one or more marker proteins that,upon expression, manifest a detectable phenotype. In particularinstances, the second vector encodes two or more marker proteins, e.g.,two or more marker proteins expressed from distinct promoters. In suchinstances, it may be that one marker protein is expressed, e.g., from abacterial or mammalian promoter and another marker protein is expressed,e.g., from a second bacterial or mammalian promoter. In certaininstances, one marker protein is expressed from bacterial promoter, andanother is expressed from a mammalian promoter.

The second vector may include one or more site-specific recombinationmotifs (e.g., complementary and/or orthogonal site-specificrecombination motifs). In some instances, the second vector includes asite-specific recombination motif capable of participating in asite-specific recombination event with the first vector of the presentinvention. In certain instances, the first vector, but not the secondvector, has a site-specific recombination motif complementary to such asite-specific recombination motif of the second vector (i.e., the secondvector does not include the complement of the motif capable ofrecombining with the first vector). It is contemplated that the secondvector may include multiple, distinct, site-specific recombinationmotifs capable of recombination with the first vector, and furthercontemplated that the presence of various recombinase enzymes maymediate which, if any, of these motifs may recombine. It is alsocontemplated that the second vector may include one or more pairs ofcomplementary site-specific recombination motifs, e.g., capable ofrecombining with each other.

The second vector may further include one or more cryptic recombinationmotifs, each including a plurality of polynucleotide segments that canbe joined to form a functional recombination motif. The crypticrecombination motif may be non-functional prior to joining of thepolynucleotide segments. For example, the second vector may undergo afirst recombination event that results in the formation of a functionalrecombination motif from the polynucleotide segments of the crypticrecombination motif. In some instances, a first and second vector caneach include one or more polynucleotide segments making up a crypticrecombination motif, such that recombination between the first andsecond vector results in joining of the polynucleotide segments to forma functional recombination motif.

The presence of complementary site-specific recombination motifs isevaluated in view of the available recombinase enzymes. In certainembodiments, the second vector includes only one of each site-specificrecombination motif capable of participating in a site-specificrecombination event with the first vector.

The second vector may include a polynucleotide segment encoding atranscriptional stop signal, such as a polyA cassette. For example, apolyA cassette may be 3′ to and fused to a framework cassette.Eukaryotic transcriptional stop signals include, e.g., a polyA additionsequence (AAAUAA) and/or a plurality of downstream nucleotides. Numeroustranscriptional stop sequences are known in the art and a variety ofthese have been used in the expression of genes from vectors. Certainarrangements involve the inclusion of a fragment including an intron anda transcriptional stop sequence following the end of a coding sequence.Examples of introns known in the art include the rabbit β-globin intronand the SV40 intron. Examples of transcriptional stop sequences includethose from SV40 or human growth hormone. Examples of combined sequencesinclude an SV40 intron/stop, the last exon of human growth hormone plusstop sequences, or the entire human growth hormone gene.

Various sets of complementary recombination motifs suitable for use inthe second vector are known in the art. For example, a pair ofcomplementary recombination motifs may include an attP motif and an attBmotif. In a second example, a pair of complementary recombination motifsmay include a hixL motif and hixR motif. Other examples of site-specificrecombination motifs include the Tn7 site-specific attTn7 motif. Otherexamples are known in the art.

In addition to the above-mentioned cassettes and other sequenceelements, the second vector of the present invention can include as anadditional functional cassette one or more stop codons. Because thevectors of the present invention, or polynucleotide segments thereof,can be expressed in multiple cell types, it is relevant that codon usageof stop codons varies across some species. For instance, the amber stopcodon (UAG) can be suppressed by certain strains of bacteria.Accordingly, it is possible to include stop codons that function incertain cell types while being read through in others, e.g., certainbacterial cell types. Exemplary stop codons that can be used selectivelyin this fashion include amber stop codons, ochre stop codons (UAA), andopal stop codons (UGA). The second vector of the present invention caninclude, e.g., an amber stop codon between the last nucleotide of a gene(e.g., a gene encoding a polypeptide as described herein) and a polyAcassette, which may, in some instances, be upstream of a cassettecapable of expressing a marker protein.

It will be appreciated by those of skill in the art that the criticalaspects of the present invention may not be limited to the presence orabsence of any one component of either of the first or second vector,but include at least the combination and the particular arrangement oftheir components such that conversion of a binding moiety occurs throughrecombination of the first vector and the second vector of the presentinvention. Further, it will be appreciated that the first vectors andthe second vectors of the invention may be interchangeable.

Multiple Vectors and Vector Libraries

In some instances, a plurality of distinct first polypeptides can beconverted to polypeptides of another type according to the methods ofthe invention simultaneously. For example, each of the firstpolypeptides may be a particular variant of a binding moiety (e.g., anantibody). A library can be constructed including a plurality of firstvectors, each encoding one of the variants, according to methods wellknown in the art. In certain instances, a library in which each vectorencodes an antibody can be constructed in which the light chain of eachof the antibodies is identical and the heavy chain of each antibody isdistinct. For example, each of the antibodies may include one or moredistinct heavy chain antigen-determining regions (e.g., CDRs). In otherinstances, a library in which each vector encodes an antibody can beconstructed in which the heavy chain of each of the antibodies isidentical and the light chain of each antibody is distinct. For example,each of the antibodies may include one or more distinct light chainantigen-determining regions (e.g., CDRs). Such libraries may, e.g., bescreened against antigens of interest (e.g., an antigen recognized bythe portion of the antibodies held constant), e.g., using methods knownin the art to identify strong-binding clones or clones showing improvedbinding affinity.

In some instances, the invention features first vectors (e.g., phagemidvectors) that may be capable of integrating with multiple distinctsecond vectors (e.g., acceptor vectors). In some instances, a firstvector includes a plurality of distinct recombination motifs (e.g., 2,3, 4, 5, 6, 7, 8, 9, 10, or more distinct recombination motifs). Therecombination motifs may be, e.g., site-specific recombination motifs.For example, the first vector may include a first site-specificrecombination motif and a second site-specific recombination motif thatis orthogonal to the first site-specific recombination motif. The firstand second site-specific recombination motifs may permit integration ofthe first vector with two distinct second vectors. Each of the integrantvectors produced by recombination of the first vector with one of thedistinct second vectors may, for example, produce a distinct chimericpolypeptide (e.g., a binding moiety of a different type from the firstpolypeptide). In one example, a second vector includes both attP andattP2 site-specific recombination motifs. In some instances, a firstvector may include an attP2 site positioned downstream of anscFv-encoding sequence but upstream of a gpIII sequence. This secondintegrase site can be used to produce fusions of the scFv to otherpolypeptides and/or polypeptide fragments (e.g., as described herein).

In some instances, the first site-specific recombination motif permitsintegration of the first vector with a second vector (e.g., an acceptorvector including a binding moiety framework) such that the resultantintegrant vector is capable of expressing an IgG including thepolypeptide (or a portion thereof) from the first vector; and the secondsite-specific recombination motif permits integration of the firstvector with a different second vector (e.g., a vector including anyfunctional domain described herein, such as a CAR), such that, forexample, the resultant integrant vector is capable of expressing an scFvfused to the functional domain. For example, the scFv may be fused to aubiquitin ligase domain, knocksideways domain, or CAR domain. The CARdomain may, for example, include a CD3-zeta or CD28 transmembranedomain, and/or a CD3-zeta, CD28, 41 BB, ICOS, FcεRIγ, influenza MP-1,VZV, and/or OX40 cytoplasmic domain, or any combination or derivativethereof. In one embodiment, the scFv is fused to a CD3-zeta domain,thereby forming an scFv-CD3-zeta fusion protein, e.g., an scFv-CD3-zetafusion protein including a transmembrane domain between the scFv and theCD3-zeta (e.g., a CD3-zeta transmembrane domain). Such an scFv-CD3-zetafusion protein may, for example, involve the scFv being presentedextracellularly by a host cell (e.g., a T cell) including the integrantvector, such that binding of the scFv to a cognate binding partnerresults in transmission of an intracellular zeta signal by the CD3-zetadomain. This may in turn, e.g., result in activation of the T cell.

Adenoviral Vectors

In some instances, a vector of the invention (e.g., a first vector orsecond vector) may be an adenoviral vector. Recombinant adenoviruses canbe generated using any means known in the art. For example, Tn7-mediatedtransposition in E. coli can be used to produce adenoviruses suitablefor use as vectors of the invention. In one example, a low copy numberE. coli plasmid containing a full-length adenoviral genome withlacZattTn7 replacing E1 is constructed. The adenovirus plasmid, or“admid,” as well as high copy number progenitors, can be stablymaintained in cells, such as E. coli (e.g., E. coli strain DH10B). Anexemplary admid system is described in Richards et al. (Cloning andExpression Vectors for Gene Function Analysis, Chapter 39: 231-240,2001), incorporated herein by reference. Transfer vectors containing amammalian expression cassette flanked by Tn7R and Tn7L can be used asdonors to transpose the mini-Tn7 into the E1 region of the adenoviralgenome. Thus, transposed recombinant admids can be readily identified bytheir β-galactosidase phenotype. Transfection of admid DNA into producercells results in the efficient production of infectious adenovirus. Thissystem may reduce the time involved in generating pure, clonal stocks ofrecombinant adenovirus without successive rounds of plaque purificationfrom 4-6 weeks to just 2-3 days.

Marker Proteins

Vectors of the present invention can include one or more markerproteins, which upon expression may permit the selection of cellscontaining the vector. Expression of a marker protein may result in themanifestation of a detectable phenotype. Examples of detectablephenotypes that may result from expression of a marker protein include,without limitation, luminescence, fluorescence, antibiotic resistance,antibiotic sensitivity, toxin resistance, toxin sensitivity, alteredgrowth rate, altered response to an analyte, altered cell structure,altered colony formation, or altered auxotrophy. Additional detectablephenotypes are known in the art. Furthermore, genes capable ofmanifesting these detectable phenotypes are also known in the art. Forexample, a detectable phenotype may result from expression of greenfluorescent protein (e.g., gfp), a red fluorescent protein (e.g., rfp),a yellow fluorescent protein (e.g., yfp), an ampicillin resistance gene(amp), a tetracycline resistance gene (tet), a kanamycin resistance gene(kan), beta galactosidase (β-gal), an alanine synthesis gene (e.g.,argA), a cystein synthesis gene (e.g., cysE), a leucine synthesis gene(e.g., lysA), a threonine synthesis gene (e.g., thrC), or any of aplurality of other natural or synthetic genes known in the art.Alternatively, the marker protein may be a functional cassette thatdirects or contributes to the expression of a gene that manifests adetectable phenotype, e.g., by expression of a transcription factor. Insuch instances, the gene that manifests the detectable phenotype may beendogenous to a cell, present on a first vector, present on a secondvector, or present on another vector. In some instances, a markerprotein (e.g., zeocin or chloramphenicol) can be used to selectintegrants by including expression elements (e.g., a promoter) on afirst vector and a marker gene on second vector, such that recombinationjoins the promoter element(s) upstream of the marker gene.

Methods for selecting or isolating cells having a detectable phenotypeare known in the art. Selecting or isolating one or more cells having aphenotype resulting from expression of a marker protein may include,depending upon the detectable phenotype, flow cytometry, culturing apopulation of cells in the presence of the relevant antibiotic or toxin,culturing a population of cells in the presence or absence of aparticular organic compound, or microscopy techniques. Additionalmethods of selecting and isolating cells having particular detectablephenotypes are known in the art.

Functional Cassettes

A vector of the invention may be suitable for expressing one or moregenes in multiple distinct cell types (e.g., bacteria, mammalian cells,and insect cells). For instance, the vector may encode one or morefunctional cassettes. A functional cassette may be, for example, anypolynucleotide segment capable of contributing to the generation,expression, or isolation of a gene (e.g., a gene encoding a bindingmoiety). A functional cassette may encode a protein or polypeptide. Thepolynucleotide segment encoding such a protein or polypeptide (e.g., abinding moiety) may be fused to a functional cassette encoding a proteinor polypeptide, such that the protein or polypeptide (e.g., bindingmoiety) is expressed as a fusion protein including the protein orpolypeptide and one or more additional amino acids encoded by one ormore functional cassettes. A functional cassette may encode a furtherprotein or polypeptide expressed independently of the protein orpolypeptide (e.g., binding moiety), meaning that, when expressed, it istranscribed as a separate transcript from any transcript encoding thefirst protein or polypeptide.

A. Regulatory Cassettes

A functional cassette may include one or more regulatory cassettes. Aregulatory cassette may be a polynucleotide segment that mediatestranscription or transcript stability, translation, or recombination.Exemplary regulatory cassettes include a regulatory sequence, such as apromoter, polyA sequence, Kozak sequence, or any other polynucleotidesequence that regulates expression (e.g., of a binding moiety). Aregulatory cassette can be a cassette that regulates expression of apolypeptide or a cassette that regulates the expression of one or moreother functional cassettes. Numerous polynucleotide segments capable ofregulating gene expression are known in the art, as are methods fortheir application in directing expression. In some instances, two ormore functional cassettes may be expressed as a fusion protein.

The expression of one or more polypeptides or functional cassettes canbe driven by various regulatory cassettes. As is known in the art,various promoters are optimized for expression in a particular celltype. For instance, some promoters are only, or substantially only,capable of driving expression when present in a bacterial cell (e.g., anE. coli lac promoter). Other promoters are only, or substantially only,capable of driving expression when present in a mammalian cell (e.g., aCMV promoter), or in an insect cell (e.g., a polyhedron promoter). Somepromoters are only, or substantially only, capable of driving expressionin still more particular subsets of cell types, while others mayfunctional broadly, e.g., in both a bacterial cell and a mammalian cell.These differences may result, in part, from the availability andfunction of distinct cellular proteins endogenous to the relevant celltypes. Furthermore, multiple promoter cassettes may be arranged suchthat a single polynucleotide segment encoding a protein or polypeptidemay be expressed in a plurality of distinct cell types, or such thatcell type can determine the expression of protein variants, each variantincluding at least a segment encoded by the same polynucleotide segment.

In some instances, a vector may include a plurality of promoters placedin series to control expression of a single gene located 3′ to thepromoters. For example, a vector may include a dual promoter element,such as catenated promoters and/or intronic promoters, as describedbelow.

(1) Catenated Promoters

Multiple promoter cassettes may be arranged in series to form a set ofcatenated promoters capable of controlling (e.g., increasing ordecreasing) the expression of a downstream gene (e.g., a gene encoding afirst polypeptide, second polypeptide, chimeric polypeptide, or anycombination or fragment thereof, of the invention), in which each of thecatenated promoters controls the expression of the downstream gene in aparticular organism. In one embodiment, two or more promoters arecatenated 5′ relative to a gene to be expressed, such that the first ATGpresent downstream of either promoter is the start codon of the gene tobe expressed. In some instances, a catenated promoter may driveexpression of a protein to be secreted. In certain instances, theprotein to be secreted includes a signal peptide that operates in bothbacterial and mammalian cells (e.g., an IL2 signal sequence). Examplesof catenated promoters are described, e.g., in Kadwell et al. (“Updateto: The Admid System: Generation of recombinant adenoviruses byTn7-mediated transposition in E. coli,” Chapter 39, Cloning andExpression Vectors for Gene Function Analysis, 2001) and Tan et al.(Genome Res. 13: 1938-1943, 2003), each of which is incorporated hereinby reference.

(2) Intronic Promoters

In another embodiment, a vector may include a promoter (e.g., aprokaryotic promoter, such as a bacterial promoter) positioned within anintron (an “intronic promoter”), such that if expressed in a eukaryoticcell (e.g., a mammalian cell or an insect cell), the promoter sequenceis spliced out of the resultant transcript. This may be desirable, forexample, if the exon located 3′ to the intronic promoter is to beexpressed under the control of the intronic promoter, but the exonlocated 5′ to the intronic promoter is not. The intron may, in certaininstances, further include additional regulatory elements or codingregions (e.g., signal peptides). For example, the intronic promoter maybe a bacterial promoter and both the 5′ exon and the 3′ exon may belocated downstream of a mammalian promoter. Thus, if the vector is in amammalian cell (e.g., a HEK-293 cell), both exons are transcribed andthe intron including the bacterial promoter is removed during RNAsplicing. If the vector is in a bacterial cell, only the 3′ exon istranscribed. As such, this dual promoter system permits the expressionof distinct variants of a particular protein in distinct cell types.

In one example of such a dual promoter system, a phagemid vector isdesigned in which an E. coli lac promoter and a bacterial signal peptideare placed within an intron of a mammalian expression cassette (FIG. 2).A promoter (e.g., a CMV promoter or an EF1a promoter) and a mammaliansignal peptide are located 5′ to this intron, and a gene encoding a VHgene is positioned in the exon located 3′ to this intron. Thus, in amammalian cell, the promoter drives the production of a VH gene fused toa mammalian signal peptide, whereas in a bacterial cell, the lacpromoter drives expression of a VH gene fused to a bacterial signalpeptide. Further vectors including such dual promoters are described,for example, in U.S. Pat. No. 7,112,439, incorporated herein byreference.

B. Signal Peptide Cassettes

The first vector can encode one or more signal peptide functionalcassettes. In some instances, the first vector encodes one or moresignal peptides 3′ of the first polypeptide. In certain instances, thefirst vector encodes one or more signal peptides 5′ of the firstpolypeptide. A signal peptide functional cassette may be fused to thefirst polypeptide or to another functional cassette. In particularinstances, the first polypeptide encoded by the first vector isexpressed in a fusion protein that includes one or more signal peptides,e.g., an N-terminal signal peptide. In some instances, a signal peptidefunctional cassette encodes a signal peptide that operates in bothbacterial and mammalian cells (e.g., an IL2 signal sequence).

In some embodiments of the present invention, the expression of one ormore signal peptides depends upon the cell in which the first vector ispresent. For instance, the first vector may encode each of a mammaliansignal peptide and a bacterial signal peptide 5′ of the firstpolypeptide. In some instances, the mammalian signal peptide is encoded5′ of the bacterial signal peptide, although the opposite order, e.g.,is also contemplated. The mammalian signal peptide may be expressed froma mammalian promoter, while the bacterial signal peptide may beexpressed from a bacterial promoter. In particular embodiments, thebacterial promoter and bacterial signal peptide functional cassette areproximal to the first polypeptide, such that expression in bacteriaresults in a fusion protein including the bacterial signal peptide andthe first polypeptide. Further, the bacterial promoter and signalpeptide cassette are flanked by splice sites, such that, in mammaliancells, expression of the mammalian promoter results in a fusion proteinincluding the mammalian signal peptide and the first polypeptide, butnot the bacterial signal peptide or promoter. In one example of such anembodiment, the first vector encodes, from 5′ to 3′, a mammalianpromoter, a mammalian signal peptide, a splice site, a bacterialpromoter, a bacterial signal peptide, a second splice site, and thefirst polypeptide.

Recombination Motifs

A segment of a nucleic acid with which a recombination motif mayparticipate in a recombination event may be referred to as acomplementary recombination motif. Site-specific recombination motifsselectively participate in recombination with complementaryrecombination motifs having a particular sequence or particular sequencecharacteristics. For example, the complementary recombination motifsattB and attP can be recombined with each other in a reaction catalyzedby, e.g., phiC31 integrase or bacteriophage lambda integrase. In someinstances, a recombination motif may be divided, having two or moreregions with particular sequence requirements separated by one or moresequences that are not substantially constrained and/or do not directlyparticipate in recombination. In some instances, complementaryrecombination motifs are identical (e.g., paired loxP sites or pairedFRT sites). In other instances, complementary recombination motifs arenon-identical. In some instances, all of the nucleotides comprising asite-specific recombination motif may be defined. In other instances,only a subset of the nucleotides comprising a site-specificrecombination motif may be defined, such as 5%, 10%, 15%, 20%, 25%, 50%,60%, 70%, 80%, 90%, 95%, 99%, or 99.5% of nucleotides present in thesite-specific recombination motif. Complementary recombination motifsmay include, e.g., a phage motif, a bacterial motif, or a direct repeatmotif. In some instances, a segment of a nucleic acid may serve as botha recombination motif and, when translated into its corresponding aminoacid sequence, a linker between two polypeptide moieties (e.g., VH andVL protein, as shown in FIG. 1).

Exemplary recombination motifs that may be used as recombination motifsin vectors of the invention include, without limitation: attB, attP,loxP, FRT, hixL, hixR and variants thereof. Variants of recombinationmotifs are known in the art (e.g., JT15, a loxP variant showingcomparable recombination efficiency to wild-type loxP), and may besubstituted and tested, e.g., in the methods and compositions describedherein. Examples of attB and attP variants with suitable recombinationefficiencies can be found, for example, in FIG. 3 of Groth et al. (PNAS97(11): 5995-6000, 2000), incorporated herein by reference. Certainrecombination motifs may be preferable for use in in vitro recombinationreactions, such as the bacteriophage lambda integrase, e.g., asdescribed in Hartley et al. (Genome Res. 10: 1788-1795, 2000), which isincorporated herein by reference. In further examples, the complementarysite-specific recombination motif pairs attB1/attP1 and attB1/attP1 canbe used in vectors of the present invention. In some instances, variantsof recombination motifs may be capable of replacing the originalrecombination motif from which the variant was derived. In otherinstances, variants of recombination motifs may not be capable ofreplacing the original recombination motif. In particular instances, thevariant recombination motifs may form distinct groups of complementaryrecombination motifs. For example, attB1 can recombine with attP1, butnot with attP2.

Recombinase Enzymes

Recombination of certain site-specific recombination motifs may befacilitated by one or more recombinase enzymes. A recombinase enzyme maybe a recombinase or integrase. A recombinase enzyme may be, e.g., aserine family recombinase or tyrosine family recombinase. As is known inthe art, the serine and tyrosine recombinase families are namedaccording to the conserved nucleophilic amino acid that interacts withDNA during recombination. Serine family recombinases include, forexample, phiC31, which recognizes attB and attP sites, HIN invertase,which recognizes hix sites, Bxb1 integrase, phiRv1 integrase, phiBT1integrase, phiFC1 integrase, and Tn3 resolvase. Bxb1 integrase, phiRv1integrase, phiBT1 integrase, and phiFC1 integrase, like phiC31integrase, may recognize attB and attP sites, and may further catalyzethe reverse reaction, e.g., in the presence of an accessory factor suchas Xis. Serine recombinases are reviewed in detail in Smith et al.(Biochem. Soc. Trans. 38: 388-394, 2010), incorporated by referenceherein. Tyrosine family recombinases include, for example, bacteriophagelambda integrase, which, like phiC31, recognizes att sites, Cre, whichrecognizes lox sites, and Flp, which recognizes frt sites. For example,bacteriophage lambda integrase, together with an integration host factor(IHF) protein, mediates recombination between an attB site and an attPsite, forming an attL and attR site (see, e.g., Hartley et al., supra).The reverse reaction (attL+attR to attB+attP) is mediated bybacteriophage lambda integrase, IHF, and excisionase (Xis).Bacteriophage lambda integrase may be particularly well-suited forrecombination performed in vitro (e.g., not within a cell). In variousembodiments of the present invention, Cre recombinase inducesrecombination between two loxP sites. In other embodiments, Flprecombinase induces recombination between two FRT sites. In someinstances, a recombinase enzyme may excise a portion of a polynucleotide(e.g., a vector). Such a recombinase enzyme may be referred to herein asan “excision enzyme.” In certain instances, an excision enzyme may beCre or Flp.

In some embodiments, phiC31 integrase is used to drive integrationbetween two vectors of the invention (FIG. 3). phiC31 integrase is asite-specific serine recombinase that recognizes 36-bp site-specificrecombination motifs (e.g., attP, attB, attL, and attR). For example,recombination of two nucleic acids, one containing an attP motif and theother containing an attB motif, by phiC31 integrase results in theintegration of the two nucleic acids at the motif sites and replacementof the attP and attB motifs with attL and attR motifs. phiC31 integrasecan also induce the reverse reaction (in which attL and attR areconverted to attP and attB, e.g., to excise an integrated nucleic acidsegment), although this may require the presence of the accessoryprotein Xis. Other recombinase enzymes that may be suitable for use inthe binding moiety conversion methods of the present invention are knownin the art.

Polypeptides

The invention provides methods and compositions for converting a firstpolypeptide into a chimeric polypeptide (e.g., a polypeptide of adifferent type). In some instances, a polypeptide (e.g., a firstpolypeptide, second polypeptide, or chimeric polypeptide) is or includesa binding moiety, such as an antibody, antibody fragment, a chimericantigen receptor, and/or a portion thereof. A polypeptide of theinvention may include or be fused to one or more functional domains(e.g., a binding moiety may be fused to the one or more functionaldomains). Exemplary functional domains to which a polypeptide of theinvention can be fused include, without limitation, a binding moiety,ubiquitin ligase domain, a knocksideways prey domain, and a markerprotein (e.g., alkaline phosphatase, lacZ, or a fluorescent protein,such as GFP, RFP, YFP, CFP, dsRed, mCherry, or any other marker proteinknown in the art). Such functional domains can be combined to impartuseful functionality to the polypeptide, e.g., as described herein.

It is appreciated that a first polypeptide, as described herein, may beused as a second polypeptide, and a second polypeptide, as describedherein, may be used as a first polypeptide.

Chimeric Polypeptides

A chimeric polypeptide of the present invention may be encoded, forexample, by an integrant vector formed upon recombination of at least afirst vector with a second vector according to the methods of theinvention. The integrant vector produced by this recombination eventincludes a polynucleotide encoding the chimeric polypeptide. Theintegrant vector may encode a single chimeric polypeptide or a set oftwo or more chimeric polypeptides, such as, for example, a heavy chainand a light chain. In some instances, the chimeric polypeptide includesat least a portion (e.g., an antigen-determining region) of a firstpolypeptide encoded by the first vector and at least a portion of asecond polypeptide (e.g., a binding moiety framework cassette) encodedby the second vector. A polynucleotide encoding a chimeric polypeptidemay also be present in a non-integrant vector. For example, thepolynucleotide encoding the chimeric polypeptide may be transferred to adifferent vector by subcloning methods known in the art.

A chimeric polypeptide of the present invention may be expressed withina cell at levels greater than, equal to, or less than the expression ofa polypeptide of the same type expressed from a vector known in the art.For example, a chimeric polypeptide encoded by a recombinant product ofthe present invention may be an IgG antibody that is expressed at alevel greater than, equal to, or less than the level at which an IgGisolated from a human and expressed from a known vector is expressed.Alternatively, a chimeric polypeptide may be expressed in vitro, forexample, using a cell-free expression system as well known in the art.

Binding Moieties

The present invention features vectors (e.g., a first vector or a secondvector) including nucleic acid sequences encoding one or morepolypeptides, or fragments thereof. The polypeptides encoded by thevectors may include, for example, binding moieties or fragments thereof.A binding moiety of the present invention may be any protein orpolypeptide capable of binding an antigen, e.g., as described herein.Certain binding moieties of the invention may include anantigen-determining region and/or a framework (e.g., a constant regionor a framework region of a variable domain).

In some instances, a binding moiety is an antibody, such as a wholeantibody, or an antibody fragment, such as an antigen-binding antibodyfragment. Alternatively, a binding moiety of the present invention maybe a protein or polypeptide that is not an antibody. A binding moietymay be, e.g., avidin, streptavidin, beta galactosidase, an affinity tag(e.g., HA, His, FLAG, SNAP, avitag, or any other peptide tag known inthe art), a short peptide tag capable of being labeled by, e.g., SFP orAcpS phosphopantetheinyl transferase (e.g., an S6 or A1 tag; see, e.g.,Zhou et al., ACS Chem. Biol. 2(5):337-346, 2007, incorporated byreference herein), a fluorescent protein (e.g., GFP, YFP, CFP, RFP,dsRed, mCherry, or any other fluorescent protein known in the art),alkaline phosphatase, a kinase, a phosphatase, a proteasomal protein, aprotein chaperone, a receptor (e.g., an innate immune receptor orsignaling peptide receptor), a chimeric antigen receptor, a synbody, anartificial antibody, a protein having a thioredoxin fold (e.g., adisulfide isomerase, DsbA, glutaredoxin, glutathione S-transferase,calsequestrin, glutathione peroxidase, or glutathione peroxiredoxin), aprotein having a fold derived from a thioredoxin fold, a repeat protein,a protein known to participate in a protein complex, a protein known inthe art as a protein capable of participating in a protein-proteininteraction, or any variant thereof (e.g., a variant that modifies thestructure or binding properties thereof). A binding moiety of thepresent invention may be any protein or polypeptide having a proteinbinding domain known in the art, including any natural or syntheticprotein that includes a protein binding domain. A binding moiety of thepresent invention may also be any protein or polypeptide having apolynucleotide binding domain known in the art, including any natural orsynthetic protein that includes a polynucleotide binding domain. Abinding moiety may include, for example, a signal peptide (e.g., abacterial signal peptide or a mammalian signal peptide) that targets itfor secretion or expression as a transmembrane protein, e.g., on thecell surface.

A binding moiety of the invention may include one or more functionaldomains (e.g., a binding moiety may be fused to the one or morefunctional domains). Exemplary functional domains to which a bindingmoiety can be fused include, without limitation, a ubiquitin ligasedomain, a knocksideways prey domain, and a marker protein (e.g.,alkaline phosphatase, lacZ, or a fluorescent protein, such as GFP, RFP,YFP, CFP, dsRed, mCherry, or any other marker protein known in the art).Such functional domains can be combined to impart useful functionalityto the binding moiety. For example, fusion of a ubiquitin ligase domainto a binding moiety may be used to ubiquinate and drive proteasomaldegradation of a target molecule to which the binding moiety is capableof binding. In a second example, a knocksideways prey domain can befused to a binding moiety such that a target molecule to which thebinding moiety is capable of binding is sequestered to a particularintracellular region (e.g., the mitochondria). In some instances, abinding moiety is an antigen receptor, such as, for example, a T-cellreceptor. In certain instances, a binding moiety is an engineeredantigen receptor or antibody. In particular embodiments, a bindingmoiety is a chimeric antigen receptor (CAR), for example, as describedin Sadelain et al. (Cancer Discovery 3: 388-398, 2013; incorporatedherein by reference) and as well known in the art. In some instances, aCAR may be suitable for expression by a T cell for use in detectingtumor associated antigens (TAAs). In certain instances, the CAR ispresented on the surface of the T cell (e.g., anchored to the T cellsurface by a transmembrane domain positioned in the plasma membrane ofthe T cell). CARs expressed by T cells generally include anextracellular TAA-specific binding moiety (e.g., an scFv composed ofantibody variable heavy and light chain genes joined by a short,flexible linker). The binding moiety of the CAR may be linked, e.g., viahinge and transmembrane domains, to an intracellular signaling domain(from, e.g., CD28, CD3ζ, or 4-1 BB). Interaction between the CAR andantigen may trigger effector functions and can, for example, mediatecytolysis of tumor cells. CAR-engineered T cells can mediate tumorregression in multiple cancers. For example, CARs directed to the CD19antigen on lymphoid malignancies have shown positive results in thetreatment of acute lymphoblastic leukemia (ALL).

In some instances, a binding moiety of the invention has been selected,cloned, isolated, sequenced, or otherwise generated or identified by amethod of screening for antibodies capable of binding one or moreparticular antigens. For example, a moiety can be a binding moietyidentified by a biopanning technique, such as phage display, ribosomedisplay, or Phage Emulsion, Secretion, and Capture (Phage ESCape). Insome embodiments, the first binding moiety is a binding moiety generatedby rational design. In various embodiments of the present invention,because biopanning often includes expression of candidate bindingmoieties from a vector, the first binding moiety of the presentinvention is a vector used to express a the first binding moiety in amethod of biopanning, examples of which include phage display, ribosomedisplay, or Phage ESCape.

The methods and compositions of the invention can also be used toconvert a binding moiety to a variant of the binding moiety having thesame or similar type. For example, the binding moiety may include aframework sequence that can be switched with an alternate frameworksequence. In some instances, the binding moiety is an antibody orantibody fragment, which is converted to an antibody or antibodyfragment of the same or similar type having a different framework. Inanother example, an antibody from a hybridoma is converted into athermal stable or cytosol-stable antibody.

Antibodies and Antibody Fragments

The vectors of the invention (e.g., first vectors, second vectors, andintegrant vectors) may encode antibodies, or fragments thereof. In someinstances, a first polypeptide encoded by a first vector is an antibodyor antibody fragment. In certain instances, a second polypeptide encodedby a second vector includes an antibody, antibody fragment, orframework. In particular instances, a chimeric polypeptide encoded by anintegrant vector encodes an antibody or antibody fragment (e.g., anantibody or antibody fragment of a different type than an antibody orantibody fragment encoded by the first vector). In some instances, anantibody or antibody fragment can be converted into another type ofpolypeptide (e.g., a CAR, ubiquitin ligase fusion, and/or knocksidewaysprey domain fusion), or vice versa, according to the methods of theinvention.

An antibody of the present invention may be a whole antibody orimmunoglobulin or an antibody fragment. An antibody may bemultispecific, e.g., bispecific. An antibody of the present inventionmay be mammalian (e.g., human or mouse), humanized, chimeric,recombinant, synthetically produced, or naturally isolated. Exemplaryantibodies of the present invention include, without limitation, IgG(e.g., IgG1, IgG2, IgG3, and IgG4), IgM, IgA (e.g., IgA1, IgA2, andIgAsec), IgD, IgE, Fab, Fab′, Fab′2, F(ab′)₂, Fd, Fv, Feb, scFv,scFv-Fc, and SMIP binding moieties. In certain embodiments, the antibodyis an scFv. The scFv may include, for example, a flexible linkerallowing the scFv to orient in different directions to enable antigenbinding. In various embodiments, the antibody may be a cytosol-stablescFv or intrabody that retains its structure and function in thereducing environment inside a cell (see, e.g., Fisher and DeLisa, J.Mol. Biol. 385(1): 299-311, 2009; incorporated by reference herein). Inparticular embodiments, the scFv is converted to an IgG or a chimericantigen receptor according to the methods described herein.

In most mammals, including humans, whole antibodies have at least twoheavy (H) chains and two light (L) chains connected by disulfide bonds.Each heavy chain consists of a heavy chain variable region (VH) and aheavy chain constant region (CH). The heavy chain constant regionconsists of three domains (CH1, CH2, and CH3) and a hinge region betweenCH1 and CH2. Each light chain consists of a light chain variable region(VL) and a light chain constant region (CL). The light chain constantregion consists of one domain, CL. The VH and VL regions can be furthersubdivided into regions of hypervariability, termed complementaritydetermining regions (CDR), interspersed with regions that are moreconserved, termed framework regions (FR). Each VH and VL is composed ofthree CDRs and four FRs, arranged from amino-terminus tocarboxy-terminus in the following order: FR1, CDR1, FR2, CDR2, FR3,CDR3, FR4. The variable regions of the heavy and light chains contain abinding domain that interacts with an antigen.

Antibodies of the present invention include all known forms ofantibodies and other protein scaffolds with antibody-like properties.For example, the antibody can be a monoclonal antibody, a polyclonalantibody, human antibody, a humanized antibody, a bispecific antibody, amonovalent antibody, a chimeric antibody, or a protein scaffold withantibody-like properties, such as fibronectin or ankyrin repeats. Theantibody can have any of the following isotypes: IgG (e.g., IgG1, IgG2,IgG3, and IgG4), IgM, IgA (e.g., IgA1, IgA2, and IgAsec), IgD, or IgE.

An antibody fragment of the present invention may include one or moresegments derived from an antibody. A segment derived from an antibodymay retain the ability to specifically bind to a particular antigen. Anantibody fragment may be, e.g., a Fab, Fab′, Fab′2, F(ab′)2, Fd, Fv,Feb, scFv, or SMIP. An antibody fragment may be, e.g., a diabody,triabody, affibody, nanobody, aptamer, domain antibody, linear antibody,single-chain antibody, or any of a variety of multispecific antibodiesthat may be formed from antibody fragments.

Examples of antibody fragments include: (i) a Fab fragment: a monovalentfragment consisting of VL, VH, CL, and CH1 domains; (ii) a F(ab′)2fragment: a bivalent fragment comprising two Fab fragments linked by adisulfide bridge at the hinge region; (iii) a Fd fragment: a fragmentconsisting of VH and CH1 domains; (iv) an Fv fragment: a fragmentconsisting of the VL and VH domains of a single arm of an antibody; (v)a dAb fragment: a fragment including VH and VL domains; (vi) a dAbfragment: a fragment that is a VH domain; (vii) a dAb fragment: afragment that is a VL domain; (viii) an isolated complementaritydetermining region (CDR); and (ix) a combination of two or more isolatedCDRs which may optionally be joined by one or more synthetic linkers.Furthermore, although the two domains of the Fv fragment, VL and VH, arecoded for by separate genes, they can be joined, using recombinantmethods, e.g., by a synthetic linker that enables them to be expressedas a single protein, of which the VL and VH regions pair to form amonovalent binding moiety (known as a single chain Fv (scFv)). Antibodyfragments may be obtained using conventional techniques known to thoseof skill in the art, and may, in some instances, be used in the samemanner as intact antibodies. Antigen-binding fragments may be producedby recombinant DNA techniques or by enzymatic or chemical cleavage ofintact immunoglobulins. An antibody fragment may further include any ofthe antibody fragments described above with the addition of additionalC-terminal amino acids, N-terminal amino acids, or amino acidsseparating individual fragments.

An antibody may be referred to as chimeric if it includes one or moreantigen-determining regions or constant regions derived from a firstspecies and one or more antigen-determining regions or constant regionsderived from a second species. Chimeric antibodies may be constructed,e.g., by genetic engineering. A chimeric antibody may includeimmunoglobulin gene segments belonging to different species (e.g., froma mouse and a human).

An antibody of the present invention may be a human antibody. A humanantibody refers to a binding moiety having variable regions in whichboth the framework and CDR regions are derived from human immunoglobulinsequences. Furthermore, if the antibody contains a constant region, theconstant region also is derived from a human immunoglobulin sequence. Ahuman antibody may include amino acid residues not identified in a humanimmunoglobulin sequence, such as one or more sequence variations, e.g.,mutations. A variation or additional amino acid may be introduced, e.g.,by human manipulation. A human antibody of the present invention is notchimeric.

An antibody of the present invention may be humanized, meaning that anantibody that includes one or more antigen-determining regions (e.g., atleast one CDR) substantially derived from a non-human immunoglobulin orantibody is manipulated to include at least one immunoglobulin domainsubstantially derived from a human immunoglobulin or antibody. Anantibody may be humanized using the conversion methods described herein,for example, by inserting antigen-recognition sequences from a non-humanantibody encoded by a first vector into a human framework encoded by asecond vector. For example, the first vector may include apolynucleotide encoding the non-human antibody (or a fragment thereof)and a site-specific recombination motif, while the second vector mayinclude a polynucleotide encoding a human framework and a site-specificrecombination complementary to a site-specific recombination motif onthe first vector. The site-specific recombination motifs may bepositioned on each vector such that a recombination event results in theinsertion of one or more antigen-determining regions from the non-humanantibody into the human framework, thereby forming a polynucleotideencoding a humanized antibody.

In particular embodiments, one or more binding moieties of the presentinvention are antibodies derived from the sequence of an antibodyexpressed by a cell (e.g., a B-cell) of an inoculated subject. Inparticular embodiments, one or more binding moieties of the presentinvention are antibodies derived from the sequence of an antibodyexpressed by a naïve cell.

In certain embodiments of the present invention, a binding moiety isbased on an alternative scaffold. Scaffolds based on different human ornon-human proteins or protein domains are known in the art (see, e.g.,Gebauer et al. 2009 Curr. Opin. Chem. Biol. 13:245-255). Differentproteins have been investigated, including affibodies, lipocalins,ankyrin-repeat proteins, natural peptide binding domains, enzymes, GFP,small disulfide-bonded peptides, protease inhibitors, and others.

Linkers

In some embodiments, a first polypeptide, second polypeptide, orchimeric polypeptide includes a linker, i.e., one or more amino acidsthat are not defined as a binding moiety constant region or as anantigen-determining region, but rather form a link between two suchregions (e.g., two constant regions, two antigen-determining regions, orone of each). The polynucleotide segment encoding the linker can bepositioned, for example, between a polynucleotide segment encoding afirst antigen-determining region and a polynucleotide segment encoding asecond antigen-determining region. In certain embodiments including alinker, the first polypeptide, second polypeptide, or chimericpolypeptide is an scFv. The polynucleotide segment encoding the linkercan include a site-specific recombination motif, e.g., a recombinationmotif of an excision motif pair or a recombination motif capable ofmediating recombination with a second vector of the present invention.In certain embodiments, each nucleotide of the polynucleotide segmentencoding the linker is translated into an amino acid of the firstpolypeptide, second polypeptide, or chimeric polypeptide. Accordingly,in certain instances, the linker is bifunctional;

that is, it is or includes a site-specific recombination motif and eachnucleotide of the linker, including the nucleotides of the site-specificrecombination motif, are transcribed and translated such that eachnucleotide corresponds to an amino acid of the binding moiety.

The present invention includes the identification, optimization, use,and/or design of bifunctional linkers. For instance, the attR sitehaving the sequence 5′-ccccaactggggtaacctttgggctccccgggcgcgtac-3′ (SEQID NO: 1) can be translated in 5 reading frames that do not contain astop codon (PNWGNLWAPRAR, SEQ ID NO: 2; PTGVTFGLPGRV, SEQ ID NO: 3;VRARGAQRLPQLG, SEQ ID NO: 4; YAPGEPKGYPSW, SEQ ID NO: 5; andTRPGSPKVTPVG, SEQ ID NO: 6) as well as a 6th reading frame that doescontain a stop codon. The generation and optimization of linkers thatboth encode a segment of a first polypeptide, second polypeptide, orchimeric polypeptide and include a site-specific recombination motif isone of the aspects of the present invention.

Chimeric Antigen Receptors

One type of polypeptide included in the present invention, e.g., as afirst polypeptide, a second polypeptide, or a chimeric polypeptide, is achimeric antigen receptor (CAR). As known in the art, CARs are chimericcell surface receptors (e.g., immunoreceptors) that include a bindingmoiety (e.g., an antibody or antibody fragment) fused to an effectordomain capable of inducing a downsteam effect in the cell expressing theCAR. In some instances, the binding moiety is displayed on the exteriorof the cell surface and the effector domain is a cytoplasmic domainfacing the interior of the cell. The binding moiety and the effectordomain are generally connected by a transmembrane domain, or stalk. Thestalk may vary in length (e.g., the length of an scFv linker or thelength of a T-cell receptor transmembrane domain). Binding between thebinding moiety and a target molecule can, in some instances, result ininduction of an intracellular signaling pathway. A CAR can be convertedto a polypeptide of another type according to the methods of the presentinvention, for example, by placing the binding moiety of the CAR, or aportion thereof, into a framework from a polypeptide of another type(e.g., an antibody or antibody fragment).

Conversely, a polypeptide of another type (e.g., an antibody or antibodyfragment) can be converted to a CAR according to the methods of thepresent invention, for example, by fusing a binding moiety from thepolypeptide of another type (e.g., one or more antigen-determiningregions from an antibody or antibody fragment) to a CAR transmembranedomain and/or one or more CAR effector domains, e.g., as describedherein.

In certain instances, a CAR is an engineered T cell receptor in whichone or more T cell receptor domains is attached to a binding moiety(e.g., an antibody or antibody fragment), such that binding of thebinding moiety to a target molecule results in activation of the T cellexpressing the CAR. The T cell may then proceed to recognize and killcells expressing the target molecule. The binding moiety of the CAR may,for example, include an antibody or antibody fragment (e.g., an scFv).The transmembrane domain may, for example, include a CD3-zeta or CD28transmembrane domain. The effector domain may, for example, include aCD3-zeta, CD28, 41 BB, ICOS, FcεRIγ, influenza MP-1, VZV, and/or OX40cytoplasmic domain, or any combination or derivative thereof. Furtherbinding moieties, transmembrane domains, and effector moieties that canbe used in CARs are known in the art. For example, antibody-modifiedCARs are described in Maus et al. (Blood 123(17): 2625-2635, 2014),incorporated herein by reference in its entirety.

In some instances, a library of CAR variants including variants of astalk region (e.g., such as a stalk described herein or as known in theart) may be generated, e.g., by the methods of the present invention.For example, a plurality of stalk variants may be generated according tomethods known in the art, and then each of the stalk variants insertedinto a CAR (e.g., between the T-cell receptor and the scFv domains of aCAR), thereby generating a library of CARs sharing identical TCR andscFv domains and variable stalks. The stalk variants may be insertedinto the CARs, for example, by the conversion methods described herein.Such a CAR library may be, in some embodiments, screened for a desiredproperty (e.g., enhanced activity in T cells). Candidate CAR variantsshowing improvement in the desired property may be selected usingscreening methods known in the art (e.g., fluorescence activated cellsorting or in vivo assays), and optionally identified by sequencing thevector expressing the selected CAR variants. This approach may beutilized to identify stalk regions that impart an improvement in such adesired property to the CAR.

Ubiquitin Ligases

A further polypeptide type that can be used in the methods andcompositions of the present invention, for example, as a firstpolypeptide, a second polypeptide, or a chimeric polypeptide, arepolypeptides including a ubiquitin ligase domain. Ubiquitin ligases(e.g., E3 ubiquitin ligases), as well known in the art, areubiquitin-conjugating enzymes that attached ubiquitin, a smallregulatory protein, to a polypeptide substrate at a lysine residue.Polyubiquitination of such a polypeptide substrate targets the substratefor degradation by the proteasome. As such, a ubiquitin ligase can beused to drive the degradation of polypeptides.

The ubiquitin conjugating domain, or ubiquitin ligase domain, of aubiquitin ligase can be attached to a binding moiety to form a“ubiquibody” capable of targeting a particular polypeptide of interestfor proteasomal degradation. For example, a binding moiety (e.g., anantibody or antibody fragment) can be fused to a ubiquitin ligase domainaccording to the methods of the present invention to form a ubiquitinthat targets the binding moiety's binding partner for degradation. Aubiquibody may be produced, for example, by recombination of a firstvector encoding a binding moiety (e.g., an antibody or antibodyfragment) and a second vector encoding a ubiquitin ligase domain,thereby forming an integrant vector encoding a chimeric polypeptide inwhich the binding moiety is fused to the ubiquitin ligase domain.Alternatively, a ubiquibody can be used as a first polypeptide of theinvention and converted to a polypeptide of another type according tothe methods of the current invention. Ubiquitin ligase domains suitablefor use in the methods and compositions of the invention include any E3ubiquitin ligase domain known in the art (e.g., a CHIP or CHIPΔTPRubiquitin ligase domain). Methods for producing ubiquibodies, andexamples thereof, are described, for example, in Portnoff et al. (J.Biol. Chem. 289(11) 7844-7855, 2014), incorporated herein in itsentirety.

Knocksideways Proteins

Polypeptides of the invention may include or be fused to a functionaldomain that promotes sequestration of the polypeptide to a particularintracellular region or compartment. For example, a polypeptide mayinclude a localization signal (e.g., a signal peptide) that directs thepolypeptide to a particular location within a cell (e.g., localizationwithin an organelle, insertion into a membrane (e.g., a cell membrane,endoplasmic reticulum membrane, mitochondrial membrane, golgi membrane,endosomal membrane, or any other cellular membrane), or secretion fromthe cell). Alternatively, a polypeptide may include or be fused to aknocksideways prey or bait domain. The knocksideways system isdescribed, e.g., in Robinson and Hirst (Curr. Protoc. Cell Biol.15.20.1-15.20.7, 2013) and Robinson et al. (Dev. Cell 18: 324-331,2010), each of which is incorporated herein in its entirety.

Briefly, the knocksideways system may be used to sequester a polypeptideof interest into a particular intracellular location (e.g., themitochondrial surface), which may, for example, inactivate thepolypeptide of interest. The polypeptide of interest may be anypolypeptide for which modulation of its intracellular location isdesired. In some instances, sequestration of the polypeptide of interestresults in functional inactivation of the polypeptide of interest. Theknocksideways system includes a bait protein and a prey protein. Thebait protein may include a sequestration domain (e.g., a mitochondrialtransmembrane domain) and a first binding moiety (e.g., an FRB domain oran FKBP domain) capable of recognizing a signal molecule (e.g.,rapamycin or a rapamycin analog, such as AP21967). The prey protein mayinclude the polypeptide of interest and a second binding moiety alsocapable of recognizing the signal molecule (e.g., an FRB domain or anFKBP domain). This second binding moiety, or portions thereof, is alsoreferred to herein as a knocksideways prey domain. As such, when thesignal molecule is present, the bait protein and the prey protein bothbind and are thus brought together. Because the bait protein issequestered to the region of the cell to which the sequestration domainis targeted, the prey protein is likewise sequestered to that region ofthe cell.

In one example, the bait protein includes an FRB domain and atransmembrane domain attached to a mitochondrial outer membrane, whilethe prey protein includes an FKBP domain and a protein to be inactivated(Robinson and Hirst, supra). In one embodiment, the bait protein is aMitotrap protein. In the absence of rapamycin or a rapamycin analog, theprey protein is free-floating within the cytosol while the bait proteinis restricted to the surface of the mitochondria. However, whenrapamycin or a rapamycin analog is added, the FRB domain and the FKBPdomain both bind to rapamycin molecules. A single rapamycin or rapamycinanalog molecule can bind to both an FRB domain and an FKBP domainsimultaneously. As a result, each rapamycin or rapamycin analog moleculecan bring bait and prey proteins together. Because the bait protein isalready restricted to the mitochondrial surface, this results insequestration of the FKBP domain-containing prey protein to themitochondrial surface as well. As such, if the protein to be inactivatedmust be localized elsewhere in the cell to function, then addition ofrapamycin or a rapamycin analog results in inactivation of the proteinto be inactivated.

The methods and compositions of the invention may be used to produceprey proteins or bait proteins suitable for use in the knocksidewayssystem—in other words, the chimeric polypeptide may be a knocksidewaysprey or bait protein. For example, a binding moiety of another type(e.g., an antibody or antibody fragment) or a first polypeptide fused toanother functional domain (e.g., a ubiquitin ligase domain or theextracellular, transmembrane, and/or intracellular domain(s) of a CAR)can be converted to a knocksideways bait or prey protein. The bindingmoiety or first polypeptide can be encoded on a first vector of theinvention, which is recombined with a second vector including aknocksideways prey or bait protein (or a portion thereof, e.g., aknocksideways prey domain), thereby producing an integrant vectorencoding a fusion protein including the binding moiety or firstpolypeptide, or a portion thereof, and the knocksideways prey or baitprotein, or portion thereof. Knocksideways prey or bait proteins mayalso serve as the first polypeptide of the methods and compositions ofthe present invention, and may therefore be converted to polypeptides ofother types according to the methods described herein.

RNA Editing

The vectors of the invention include polynucleotide segments encodingpolypeptides (e.g., first polypeptides, second polypeptides, andchimeric polypeptides). These polynucleotide segments may include, forexample, introns, exons, and various regulatory and non-coding elements.In some instances, the non-coding elements include one or more sitesthat, once transcribed to RNA, are capable of undergoing RNA editing. Asknown in the art, RNA editing is generally performed by an RNA editingenzyme, such as an adenosine deaminase acting on RNA (ADAR) enzyme.Briefly, ADAR enzymes catalyze the conversion of adenosines to inosinesin double-stranded RNA substrates. Inosine mimics the properties ofguanosine and therefore preferentially forms base pairs with cytosine.As such, the adenosine-to-inosine conversion catalyzed by an ADAR enzymeeffectively results in an A-to-G single nucleotide polymorphism in theRNA, which can alter, for example, the amino acid sequence encoded bythe RNA, RNA splicing, translational efficiency, RNA half-life, capacityof the RNA to hybridize to another polynucleotide (e.g., bindingcapacity or specificity of an siRNA, shRNA, miRNA, or other RNA for atarget polynucleotide), and/or any other factors impacted by thenucleotide sequence of an RNA molecule as known in the art.

An ADAR enzyme may be present in a solution containing a vector of theinvention, or the vector and the ADAR enzyme can both be present withina cell. In some instances, the vector of the invention includes apolynucleotide encoding an ADAR enzyme. In some instances, the ADARenzyme is encoded in another vector or in the genome of the cell. ADARenzymes may induce adenosine-to-inosine conversion in double-strandedRNAs (e.g., a self-hybridized RNA strand or two RNA strands hybridizedto each other). In some instances, a vector of the invention includes apolynucleotide segment encoding a polypeptide (e.g., a firstpolypeptide, second polypeptide, or chimeric polypeptide), which istranscribed to produce an mRNA transcript. The mRNA transcript may, incertain instances, be capable of self-hybridization to form adouble-stranded RNA molecule. For example, the mRNA transcript mayinclude a first region and a second region capable of hybridizing to thefirst region to form a duplex. Such double-stranded RNA regions capableof being edited by ADAR enzymes are known in the art. In a firstexample, long double-stranded RNAs including at least about 100 basepairs (bp) (e.g., at least 100 bp, 110 bp, 120 bp, 130 bp, 140 bp, 150bp, 175 bp, 200 bp, 250 bp, 300 bp, 400 bp, 500 bp, 600 bp, 700 bp, 800bp, 900 bp, 1000 bp, 1250 bp, 1500 bp, 1750 bp, 2000 bp, 2500 bp, 3000bp, 4000 bp, 5000 bp, 6000 bp, 7000 bp, 8000 bp, 9000 bp, 10,000 bp, ormore) may be edited promiscuously (i.e., at adenosine residuesthroughout the sequence). In certain instances, about 50% of alladenosine residues in such a long double-stranded RNA may be convertedto inosines. In a second example, short double-stranded RNAs (e.g., RNAsincluding about 1-100 bp; preferably RNAs including about 20-30 bp,e.g., about 20 bp, 21 bp, 22 bp, 23 bp, 24 bp, 25 bp, 26 bp, 27 bp, 28bp, 29 bp, and 30 bp) include one or more specific editing-sitecomplementary sequences (ECS), which form an imperfect fold-backdouble-stranded RNA structure between the exon sequence surrounding anadenosine-to-inosine editing site and a downstream (e.g., intronic)complementary sequence. Such ECSes can be, for example, used forsite-specific RNA editing. In a third example, a double-stranded RNAregion greater than about 30 bp in length (e.g., at least 30 bp, 40 bp,50 bp, 60 bp, 70 bp, 80 bp, 90 bp, or 100 bp, or more) may include oneor more mismatched bases, bulges or loops. In this example, adenosineresidues in the sequence can be, e.g., selectively edited to inosines.

Exemplary RNA editing enzymes useful in the methods and compositions ofthe invention include, without limitation, mammalian ADAR1, ADAR2, andADAR3; Caenorhabditis elegans CeADR1 and CeADR2, Drosophila ADAR,chicken ADAR, zebrafish ADAR, sea urchin ADAR, sea anemone ADAR, anyother ADAR known in the art, adenosine deaminases acting on tRNAs(ADATs), and prokaryotic tRNA adenosine deaminase (TadA) enzymes.Exemplary RNA editing enzymes and mechanics through which such enzymesperform RNA editing are described, for example, in Nishikura (Annu. Rev.Biochem. 79:2.1-2.29, 2010), Savva et al. (Genome Biol. 13:252, 2012),and Schoft et al. (Nuc. Acids Res. 35(11): 3723-3732, 2007), each ofwhich is incorporated by reference herein in its entirety. In someinstances, an mRNA can be edited after transcription by programmedtranslational bypassing, by which a ribosome bypasses an interval of themRNA sequence (see, e.g., Lang et al., PNAS 111(16): 5926-5931, 2014;incorporated herein by reference). For example, an mRNA encoded by avector of the invention (e.g., an mRNA encoding a first polypeptide,second polypeptide, or chimeric polypeptide) may include one or moretranslational bypassing elements (byps), e.g., including a takeoff codonupstream of a stop codon followed by a sequence capable of forming ahairpin, as well as a matching landing triplet, e.g., about 50nucleotides downstream.

Cells

The present invention provides methods and compositions for converting afirst polypeptide, or fragment thereof, into a second polypeptide, orfragment thereof. The methods of the invention may be performed in acell. For example, two vectors, one encoding a first polypeptide, andthe other encoding a second polypeptide, can be recombined in a cell(e.g., a cell expressing a recombinase enzyme) to form an integrantvector encoding a chimeric polypeptide including the first polypeptide,or a fragment thereof, and the second polypeptide, or a fragmentthereof. The compositions of the invention may include a cell (e.g., acell including one or both of a first vector and a second vector of theinvention). In some instances, the cell includes a recombinase enzymecapable of recombining the first vector and the second vector, e.g.,according to the methods of the invention. A cell of the presentinvention may be any manipulable cell known in the art, such as a celldescending from a laboratory, commercial, or industrial cell line knownin the art. A cell may be an archaeal cell, bacterial cell, fungal cell,or eukaryotic cell. A cell may be a yeast cell, plant cell, or animalcell. In some instances, the cell may be an E. coli cell, S. cerevisiaecell, or animal cell. The cell may be, e.g., a mammalian cell such as ahuman cell. Alternatively, the cell may be, for example, an insect cell(e.g., a Drosophila cell). A cell may be an immortalized cell.Alternatively, a cell may be a non-immortalized cell. Because thevectors of the present invention may include multiple promoters capableof driving each of one or more proteins or polypeptides encoded by thevectors in any of one, two, or more types of cells, the vectors of thepresent invention may be capable of expressing one or more proteins ineach of one or more different cell types in accordance with thearrangement of promoters, splice sites, and other expression-determiningsequences. It is understood that in various embodiments of the presentinvention, the first, second, and/or recombinant vectors of the presentinvention are intended to express one or more proteins or polypeptidesin each of two or more cell types.

In order for site-specific recombination to occur within a cell of thepresent invention, the cell must include a recombinase enzyme. One ormore recombinase enzymes of the present invention may be desired, in aparticular recombination reaction, based upon the particularsite-specific recombination sites present on the first vector and/orsecond vector. For instance, a first recombinase enzyme may be used forrecombination between the first vector and second vector, while adifferent recombinase enzyme may be used to mediate an excision event. Arecombinase enzyme may be endogenous to a cell (i.e., naturally encodedby the genome of that cell) or may be transgenic (i.e., introduced by atechnique of molecular biology). A transgenic recombinase enzymeexpressed in a cell may be expressed from a vector, such as a first orsecond vector of the present invention or another vector.

A recombinase enzyme may be any recombinase known in the art. In someinstances, a recombinase enzyme may be an integrase. In certaininstances, a recombinase enzyme may be a serine family recombinase ortyrosine family recombinase. The serine and tyrosine recombinasefamilies are each named according to the conserved nucleophilic aminoacid that interacts with DNA during recombination. Serine familyrecombinases include, for example, phiC31 integrase, which recognizesatt sites, HIN invertase, which recognizes hix sites, and Tn3 resolvase.Tyrosine family recombinases include, for example, lambda integrase,which recognizes att sites, Cre, which recognizes lox sites, and FLP,which recognizes frt sites. Other recombinase enzymes are known in theart. For the purposes of the present invention, a recombinase enzymecapable of facilitating recombination of complementary recombinationmotifs present in one or more vectors of the present invention may beselected.

The invention includes various combinations of recombinase enzymes,e.g., recombinases and integrases. In some instances a plurality ofrecombinase enzymes are expressed in the same cell at the same time andfunction independently.

In Vitro Conversion

The present invention provides methods and compositions for converting afirst polypeptide, or fragment thereof, into a chimeric polypeptide. Theconversion methods of the invention may be performed in vitro (e.g.,outside of a cell, such as in a cell-free system). In one example, twovectors, one encoding a first polypeptide and the other encoding asecond polypeptide, can be recombined in a solution (e.g., a solutionincluding a first vector, a second vector, and a recombinase enzyme ofthe invention) to form an integrant vector encoding a chimericpolypeptide including the first polypeptide, or a fragment thereof, andthe second polypeptide, or a fragment thereof. The solution may includeadditional factors, reagents, and/or buffers that may enable therecombinase enzyme to successfully catalyze the recombination reaction(e.g., as known in the art). In some embodiments, multiple instances ofthe method can be performed in parallel using multiplexed systems asknown in the art. For example, parallel reactions can be run inoil-in-water emulsion droplets, multiwell plates, multiple tubes, orother systems including multiple compartments.

The compositions of the invention may include one or both of a firstvector and a second vector of the invention. In some instances, thecomposition includes a recombinase enzyme capable of recombining thefirst vector and the second vector, e.g., according to the methods ofthe invention. In certain instances, the composition may not include acell, or may include a cell not containing the first vector, secondvector, and/or recombinase enzyme. In some instances, the compositionsof the invention may include multiple compartments, each containing afirst vector, a second vector, and/or a recombinase enzyme, such thatthe first vector of each compartment may recombine with the secondvector of that compartment according to the methods of the invention,thereby resulting in multiple conversion reactions occurring inparallel.

In one example, a solution is provided containing a first vector, asecond vector, and a recombinase enzyme. The first vector includes apolynucleotide encoding a first polypeptide and a site-specificrecombination site (e.g., an attP site). For example, the firstpolypeptide may be an scFv and the attP site may be located within thepolynucleotide encoding the linker region of the scFv. The first vectormay further include one or more additional polypeptide-encoding elements(e.g., a polynucleotide encoding a CH or CL domain). The second vectorincludes a polynucleotide encoding a second polypeptide and asite-specific recombination site (e.g., an attB site). For example, thesecond polypeptide may include portions of an IgG (e.g., a CL domain).The attB site may be positioned upstream of the CL domain. Therecombinase enzyme (e.g., bacteriophage lambda integrase or phiC31integrase) is capable of recombining the site-specific recombinationsites of the first vector and the second vector. The solution mayfurther include, e.g., accessory factors (e.g., Xis excisionase andintegration host factor (IHF)), reagents (e.g., spermidine and BSA),buffers and solutes (e.g., Tris HCl, NaCl, and EDTA). For example, thesolution may include 25 mM Tris Hcl pH 7.5, 22 mM NaCl, 5 mM EDTA, 5 mMspermidine HCl, and 1 mg/mL BSA (e.g., as described in Hartley et al.,supra). Recombination between the first vector and the second vector bythe recombinase enzyme results in the formation of an integrant vectorencoding a chimeric polypeptide (e.g., an IgG including the variabledomains of the scFv, the CH domain of the first vector, and the CLdomain of the second vector) including at least a portion of the firstpolypeptide fused to at least a portion of the second polypeptide.

Arrangements of Polypeptide-Encoding Sequences and Functional Cassettesfor Achieving Conversion

An important aspect of the present invention is that the components ofthe first polypeptide and components of the second polypeptide arepositioned such that recombination between the first and second vectorsresults in a functional chimeric polypeptide, e.g., of a type differentfrom that of the first binding moiety. The description and examplesprovided herein provide sufficient information for the construction of awide variety of first and second vectors capable of recombining in sucha manner. Without limiting the scope of the present invention, a numberof first and second vector pairs are described herein as illustrativeexamples.

In one embodiment, the first polypeptide encoded by the first vector isan scFv including, from 5′ to 3′, an immunoglobulin light chain (VL), alinker, and a variable region of an immunoglobulin heavy chain (VH). Thefirst vector includes a promoter capable of directing expression of thescFv, such as a bifunctional promoter or trifunctional promoter.Importantly, the linker of the scFv of the first vector is bifunctional,capable of being translated into an amino acid linker positioned betweenthe VL and VH and also encoding a site-specific recombination motif. Thefirst vector additionally includes, 3′ and separate from thepolynucleotide segment encoding the scFv, an CH cassette and a polyAcassette. The polynucleotide segment encoding the CH and polyA isseparated from the polynucleotide segment encoding the scFv by aplurality of nucleotides. These nucleotides are flanked an excisionmotif pair (e.g., loxP sites). The second vector of this embodimentincludes a site-specific recombination site complementary to that of thelinker. The second vector encodes, 5′ of the site-specific recombinationsite, a promoter, such as a bifunctional or trifunctional promoter. Italso encodes, 3′ of the site-specific recombination site, a polyAcassette and an immunoglobulin light chain constant region cassette. Tworecombination events in this embodiment mediate the conversion of thescFv to an immunoglobulin. In one event, recombination between thesite-specific recombination motifs of the excision motif pair (e.g., bya Cre recombinase enzyme) excises the plurality of polynucleotidesbetween the VH of the scFv of the first binding moiety and the CH of thefirst binding moiety. This event brings together the VH, CH, and PolyAto form a substantial portion of an immunoglobulin heavy chain. Inanother event, which may occur before, after or concurrently with theexcision event, the site-specific recombination motif present in thelinker of the first binding moiety recombines with the site-specificrecombination motif of the second vector. This event separates the VHand VL of the scFv and instead associates the VH with the promoter ofthe second vector, completing an expressible immunoglobulin heavy chainconstruct. In addition, the VL of the scFv becomes associated with thelight chain constant region and polyA of the second vector, completingan expressible immunoglobulin light chain construct.

Depending on the site-specific recombination motifs present in thedescribed vectors, it is understood that the described recombinationevents may occur in the presence of any of one or more particulardesired recombinase enzymes. It is appreciated that many if not all of awide variety of known site-specific recombination motifs and associatedenzymes are appropriate to the uses of the present invention. It isadditionally appreciated that any or all of the recombination motifs orhybrid motifs left following recombination may be bifunctional (aminoacid-encoding) in this or other methods of the present invention.

Kits

The vectors, libraries, cells (e.g., E. coli strains), recombinaseenzymes, and/or other materials described herein may be assembled into akit. The kit may include instructions for producing chimericpolypeptides according to the methods of the invention.

EXAMPLES

The below exemplary methods shall not limit the scope of the inventionas otherwise described above. The below exemplary methods illustrate asubset of the presently invented methods.

Example 1: Conversion of an scFv Binding Moiety into an IgG BindingMoiety

Binding moieties capable of binding one or more particular antigens maybe identified by biopanning techniques such as phage display. Manybinding moieties identified by such techniques are single-chain bindingmoieties, such as an scFv. However, IgG molecules may be desirable forcertain applications, e.g., for reasons related to stability, commercialpreferences, research preferences, potential for integration orcombination with existing or developing technologies, and increasedbinding of antigens, due, e.g., due to the avidity effect. Single-chainantibodies can be converted to IgG type antibodies by methods involvingsub-cloning. This can involve substantial time and expense. This Exampledescribes the conversion of an scFv, e.g., an scFv identified by displaybiopanning as having high affinity for a particular antigen, into an IgGmolecule. The method utilizes recombination between a first vector and asecond vector within E. coli. More specifically, the scFv is encoded bya first vector and is converted to an IgG by recombination between thisfirst vector and a second vector that includes an IgG framework. Therecombinant product of this recombination is capable of expressing anIgG light chain and an IgG heavy chain (together, an IgG molecule), eachincluding an antigen-determining region originating from the scFv.Importantly, this IgG molecule was not encoded by the first vector, thesecond vector, or the first and second vector when taken as a pair. Therecombinant product is capable of expressing the IgG molecule in amammalian cell, e.g., for production purposes.

As summarized in FIG. 4, the first vector (Vector 1 of FIG. 4A) is aphagemid donor vector including an scFv binding moiety that is fused toGpIII (together, an scFv fusion protein). This first vector is a vectorhaving been identified in a phage display biopanning procedure forphagemids encoding an scFv capable of binding a particular antigen. Thecomponents of the scFv binding moiety, shown within a box, include avariable region of an immunoglobulin light chain (VL), a linker, and avariable region of an immunoglobulin heavy chain (VH). Importantly, thelinker of the scFv of vector 1 is bifunctional. It encodes the scFvlinker of 12 or more amino acids and additionally encodes asite-specific recombination site that is a substrate of phiC31 (attP′).The phiC31 integrase is from Streptomyces phiC31 and is an enzyme thatmediates unidirectional, site-specific recombination betweencomplementary site-specific recombination sites, namely the 36 bp phageattachment site, attP, and the 36 bp bacterial attachment site, attB.The attP′ of the scFv linker is optimized from a known attP site forbifunctional use.

Positioned 5′ of the scFv fusion protein, the first vector encodes, from5′ to 3′, a first CMV promoter (P_(cmv1)), a mammalian signal peptide(mSigP), a first splice site (5′ ss), a lac operon promoter (P_(LacOP)),a bacterial signal peptide (bSigP), and a second splice site (3′ ss). Asa result of this arrangement, expression from P_(cmv1), e.g., in amammalian cell, results in an scFv protein that includes a mammaliansignal peptide but not a bacterial signal peptide, while expression fromP_(LacOP) results in an scFv fusion protein that includes a bacterialsignal peptide but not a mammalian signal peptide. It is to beunderstood that modification of polynucleotides 3′ of these promoter andsignal peptide functional cassettes may modify the translated proteinwithout altering the basic effect of this arrangement, namely thecell-specific translation of a protein having one or the other of thetwo signal peptides.

Positioned 3′ of the scFv, the first vector encodes, from 5′ to 3′, asite-specific recombination site that is a substrate of Cre recombinase(loxP, e.g., JT15), an amber stop codon (not shown), a cassette encodingthe phage M13 gene 3 product (GpIII), a B. subtilis SacR promoter(PsacR), a selectable marker (SacB), a chimeric trp and lac promoter(P_(tac)), a selectable marker (LacZα), a second substrate of crerecombinase (loxP), a polynucleotide segment encoding the second andthird constant domains of an IgG heavy chain (CH; it is noted that whileCH can mean a binding moiety including two each of the second and thirdconstant domains of an immunoglobulin, it is here used within thisexample to mean an immunoglobulin antibody chain fragment that includesone of each), an amber stop codon, and a polyadenylation sequence(polyA; not shown). In some instances, a zeocine gene is present betweenthe amber stop codon and the polyA. The amber stop codon positionedbetween the scFv and the GpIII gene allows expression of the scFv innon-suppressing E. coli hosts.

The loxP sites of the first vector are an excision motif pair. Excisionoccurs in the presence of the loxP site recombinase enzyme Crerecombinase. Cre recombinase is a tyrosine recombinase enzyme derivedfrom the P1 bacteriophage. Cre recombinase catalyzes the site-specificrecombination of loxP sites, which are 34 bp sites that include two 13bp palindromic sequences that flank and 8 bp spacer region. The productof the recombination of loxP sites depends upon the location andrelative orientation of the loxP sites. DNA between two loxP sites thatare oriented in the same direction is excised as a circular loop of DNA,as occurs in the present example. As a result of the present arrangementof loxP sites, incubating the first vector with cre recombinase resultsin excision of the nucleotides flanked by the loxP sites (FIGS. 4B and4C). Also, as shown in FIG. 4C, the excision event leaves a hybrid loxPsite in the excision product.

The first vector is transferred into E. coli. In some embodimentsrepresented by the present example, the first vector is transformed intothe E. coli cell. In other embodiments represented by the presentexample, the first vector is transduced into the E. coli cell, in whichinstances the E. coli cell is an F⁺ E. coli cell. The E. coli cell intowhich the first vector is transduced includes a second vector (FIG. 4B).The second vector encodes, from 5′ to 3′, a CMV promoter (P_(CMV)2), amammalian signal peptide (mSigP), a 36 bp site-specific recombinationsite that is a substrate of phiC31 integrase and that is complementaryto attP′ (attB), an immunoglobulin light chain constant region, an amberstop codon, a polyadenylation sequence (polyA), and a zeocin resistanceprotein (Zeo). The zeocin resistance cassette confers selection in bothmammalian cells and in E. coli. In some instances, the zeocin resistancecassette is used to replace an ampicillin resistance cassette that maybe present in the first vector prior to the steps described in thepresent example. In other instances, the zeocin resistance cassette maybe replaced by an alternate resistance cassette (e.g., a CamR cassette).In certain instances, a polyadenylation signal site (polyA) is present3′ of the attB site. In particular instances, a variable chain constantregion is present between the attB site and the polyA.

In addition to the second vector, the E. coli cell into which the firstvector is transformed includes, for example, cre recombinase and phiC31integrase. As described, and as is known in the art, cre recombinase iscapable of mediating site-specific recombination between loxP sites andphiC31 integrase is capable of mediating site-specific recombinationbetween attP′ and attB. Accordingly, if the first and second vectors ofthis example are present together in the cell, at least tworecombination events occur within the cell. It is not specified in thepresent example whether one or both of the phiC31 integrase and the crerecombinase are endogenous to the E. coli cell or introduced to the E.coli cell by techniques of molecular biology, e.g., by integration orexpression from the first vector, the second vector, or one or moreother vectors. It is further not specified whether these elements areconstitutively or inducibly expressed. Accordingly, in some embodimentsthe Cre recombinase mediated and phiC31 integrase mediated recombinationevents may occur in any order or simultaneously. In some embodiments ofthe present invention, the order may be wholly or partially regulated orcontrolled. However, such regulation or control may not be necessary.

In one example, Cre recombinase is expressed in a vector (e.g., a pAX889vector). The Cre gene may be placed under the control of an induciblepromoter such as, for example, the arabinose-inducible araC promoter ina vector carrying a different replication origin and antibioticresistance gene (e.g., p15A origin and spectinomycin resistance) thanthe phagemid, so both plasmids can be maintained in the same E. colicell. The pAX889 vector was tested using TG1 cells transformed withpAX889, which were infected with phage carrying a phagemid with two loxPsites as direct repeats flanking a 300 bp locus. In the presence of 2%arabinose (which induces Cre expression), the phagemid underwentintramolecular recombination to yield products with the interveningregion deleted.

Cre recombinase mediates recombination between the loxP sites of thefirst vector, resulting in excision of the polynucleotide segmentsencoding GpIII, P_(SacR), SacB, P_(tac), and LacZα. In FIG. 4B, dashedlines form a bracket that indicates the excised segment. Furthermore,following excision, the number of nucleotides separating thepolynucleotide segment encoding the scFv binding moiety and the CHcassette is greatly reduced. As shown in FIG. 4C, the VH and CH are yetseparated by at least the hybrid loxP site remaining at the point ofrecombination following the excision event. More specifically, the CH isfused to the VH of the scFv such that the VH and CH could be expressedas a single protein (together, a VH-CH fusion protein). For instance,the nucleotides separating the VH and CH after excision could encodeamino acids when transcribed and translated in frame with the VH and CH.Alternatively, the nucleotides intervening between polynucleotidesegments encoding the VH and CH could include splice sites, such thattranscription of the polynucleotide segments encoding the VH and CH in asingle transcript could result in a mature mRNA capable of expressing asingle protein including the VH and CH. In a VH-CH fusion protein soexpressed, the terminal amino acids of the VH and CH may be directlyadjacent or separated by one or more amino acids encoded by interveningnucleotides. Excision can be monitored for occurrence or efficiency byscreening for phenotypes connected with the SacB and a LacZα cassettes.In particular, cells in which one or all first vectors have undergoneexcision survive on sucrose due to loss of SacB and will thus appearwhite, rather than blue, when cultured in the presence of the LacZsubstrate X-gal.

In the phiC31 integrase-mediated recombination event, the attP′site-specific recombination motif of the first vector and the attBsite-specific recombination motif of the second vector recombine togenerate a recombinant product (e.g., a recombinant product in which oneor more regulatory elements are introduced to control expression of agene expressing, for example, an VH-CH fusion protein). In someinstances, regulatory elements (e.g., a mammalian and/or bacterialpromoter, and a functional protein initiation site) are added 5′ to theVH-CH fusion protein-encoding gene. As shown in FIG. 4B, thisrecombination event results in crossover between the first vector(within the linker) and second vector (between the mammalian signalpeptide and the polyA). When this recombination event occurs, incombination with the above-described excision event of the presentexample, a polynucleotide segment encoding a chimeric polypeptide isgenerated. As shown in FIG. 4C, this encoded chimeric polypeptideincludes two separately expressed proteins: a protein including the VLof the scFv and an (not shown) immunoglobulin light chain constantregion (an immunoglobulin light chain) and protein that includes the VHof the scFv and an immunoglobulin heavy chain CH (an IgG heavy chain).Accordingly, the first binding moiety, an scFv, has been converted to animmunoglobulin having two chains, each chain including a portion of thescFv.

To generalize some of the major events entailed by the conversion of thepresent example, one can look to the general results of each of the tworecombination events. The Cre recombinase-mediated excision eventresults in an scFv fusion protein that includes the CH. This fusionprotein includes all of the constant and antigen-determining regions ofan immunoglobulin heavy chain (VH and CH). However, it further includesthe light chain antigen-determining region, VL. The linker separatingthe VL from the VH includes an attP′ recombination motif. Whenrecombination with the second vector attB motif occurs, the VL isseparated from the VH and CH, and is fused with a light chain constantregion (LC) encoded by the second vector. As a result of theserecombination events together, the recombinant product includes animmunoglobulin light chain and an immunoglobulin heavy chain that areseparately expressed. Accordingly, the scFv has been converted to animmunoglobulin. While this brief description does not capture everyadvantage of the present invention, it provides a basic overview of thegeneral mechanism of one embodiment.

With reference to the other functional cassettes of the first and secondvector, the following occur in the present example. The segment of thefirst vector encoding P_(CMV1), mSigP, 5′ ss, P_(LacOP), bSigP, and 3′ss remains associated with VL. After recombination with the secondvector, the VL is followed by an attL′ hybrid recombination motif, amberstop codon, polyA derived from the second vector, and zeocin resistancecassette derived from the second vector. Separately, the CH and polyA ofthe first vector remain associated with the VH. After recombination withthe second vector, the VH is preceded by the Pcmv2 promoter derived fromthe second vector, a mammalian signal peptide derived from the secondvector (not shown), and an attR hybrid recombination motif. Thus, boththe immunoglobulin light chain and the immunoglobulin heavy chain of thechimeric polypeptide may be expressed in mammalian cells. While notexplicitly noted in FIG. 4, the recombinant product includes functionalprotein initiation sequences 5′ of the polynucleotide segment encodingeach immunoglobulin chain of the chimeric polypeptide. It iscontemplated that in various embodiments of the present invention thechimeric polypeptide protein or proteins may include promoters and othersequence elements for expression in any of one or more of bacterialcells, insect cells, or mammalian cells.

Example 2: Bifunctional Expression Constructs

The present example relates the use of a particular bifunctionalexpression construct for use within the technique of Example 1. As usedin the present examples, an expression construct means a combination ofregulatory elements directed to the expression of a particular proteinor a set of variants of that protein.

It is known that the requirements for the expression of proteins in,e.g., bacteria, mammalian cells, and insect cells can differ.Furthermore, it is known that the requirements for expression can varyamong bacteria, among mammalian cells, and among insect cells. Anexpression construct may be a bifunctional expression construct suchthat the particular protein or set of variants of that protein can beexpressed in both mammalian cells and bacterial cells. The presentexample includes a human IgG1 framework as the first vector Fc andsecond vector LC because human IgG is one of a variety of frameworks oftherapeutic value, e.g., for use against pathogens and cancer cells.

With respect to the bifunctional expression construct of the presentexample, the construct includes a cassette based on the strongcytomegalovirus (CMV) promoter. This CMV promoter is sub-cloned 5′ ofthe scFv of a phagemid similar to that of Example 1. The constructfurther includes a cassette based on the mammalian promoter shown inFIG. 2. The CMV promoter is positioned 5′ of a mammalian IgG heavy chainsecretion signal that includes an intron, which can then be expressedfrom the CMV promoter. The mammalian intron contains the lacpromoter/operator. Positioned 3′ of the lac promoter/operator, and stillwithin the mammalian intron, is a polynucleotide segment encoding abacterial signal peptide. The bacterial signal peptide sequence overlapswith a splice acceptor site (see Quinlan et al., J. Biol. Chem. 288:18803-10, 2013; incorporated herein by reference). The bacterialpromoter, signal peptide, and splice sites can be or include previouslycharacterized consensus sequences that are well known in the art. Thebacterial signal peptide is a pelB signal peptide having a consensussplice acceptor site known to support Fab production in the E. coliperiplasm and to be spliced efficiently in mammalian cells (see U.S.Pat. No. 7,112,439, incorporated herein by reference). The intronnucleotide sequence may be designed using, for example, promoterconsensus sequences, signal sequence consensus sequences, and splicesite consensus sequences well-known in the art (see, e.g., Mergulhao etal., Biotechnology Advances 23: 177-202, 2005; Stern et al., Trends CellMol. Biol. 2: 1-17, 2007; and Jackson, Nucleic Acids Res. 19: 3795-3798,1991; each of which is incorporated herein by reference).

Within E. coli, this expression construct may express, from thebacterial promoter within the mammalian intron, an scFv proteinincluding a bacterial signal peptide. This protein may be present, f forexample, in the bacterial periplasm. This protein may be displayed onthe surface of a virus (e.g., M13 bacteriophage), for example, as afusion to a coat protein (e.g., GpIII). The same expression construct ina mammalian cell may splice out the bacterial promoter/operator andsignal peptide sequence, resulting in the expression of an scFv proteinincluding the mammalian signal peptide.

Proper expression of proteins in particular cell types may furtherinvolve a polyadenylation signal. In the present example, each of thefirst and second vector includes a polyadenylation signal that is theSV40 polyadenylation signal. This signal is isolated or synthesized andcloned, e.g., 3′ of the Fc cassette, which is a human IgG1 Fc.

Example 3: Trifunctional Expression Constructs

Binding moieties, e.g., first polypeptides, second polypeptides, andchimeric polypeptides, of the present invention can be expressed fromtrifunctional expression constructs. In particular, it is known that therequirements for the expression of proteins in, e.g., bacteria,mammalian cells, and insect cells can differ. Furthermore, it is knownthat the requirements for expression can vary among bacteria, amongmammalian cells, and among insect cells. An expression construct may bea trifunctional expression construct such that it is capable ofpromoting the expression of a particular protein or set of variants ofthat protein in mammalian cells, bacterial cells, and insect cells.

A variety of functional cassettes may be utilized in a multifunctionalexpression construct. These cassettes include the CMV intron/enhancerregion (CMV IE), polyhedron promoter (P_(PH), from baculovirus), tacpromoter (P_(tac)), bacteriophage T7 promoter (P_(T7)), P_(CMV) promoter(complete sequence not shown in FIG. 5), E. coli ribosome binding site(RBS), and Kozak sequence. FIG. 5 shows an arrangement of thesefunctional polynucleotide cassettes leading up to a protein translationATG start site (Net). The arrangement includes the removal of all ATGsequences from the cassettes, in order to eliminate the presence ofpotential Net protein initiation sites from within the trifunctionalexpression construct. As shown these cassettes are assembled, from 5′ to3′, in the order of P_(CMV), CMV IE, P_(polyhedron), P_(tac), P_(T7),RBS, Sfil restriction site, and Kozak, the last being immediately priorto fMet. This concatenation of CMV, polyhedron, and Lac promotersenables a single multifunctional expression construct capable ofexpressing a protein from a single coding sequence in any of three typesof hosts: mammals, insects, and bacteria.

Example 4: Validation of Transformation or Transduction of E. Coli withthe First Vector and Second Vector

The first and second vectors of Examples 1 and 2 may include amber stopcodons. These amber stop codons can be suppressed in TG1 E. coli cells.TG1 cells can be TG1 cells that express Cre and PhiC31. According to thepresent example, the techniques presented in Examples 1 and 2 areexecuted using TG1 E. coli cells. TG1 cells successfully transformed ortransduced with the second vector can be positively selected by growthin the presence of zeocin.

TG1 cells successfully transformed or transduced with the first vectorcan be identified by response to growth on 6% sucrose. TG1 cellsexpressing SacB fail to grow on the sucrose media. Accordingly,transformed or transduced TG1 cells are grown in duplicate by patchingor replica plating on plates with and without 6% sucrose to distinguishcells that do or do not express SacB. Transformed or transduced TG1cells can also, or alternatively, be patched, replica plated, or grownonto plates containing X-gal and IPTG to confirm expression of the LacZαgene by blue white selection.

Example 5: Optimization of a Bifunctional Att Site-SpecificRecombination Sites

In various embodiments of the present invention, a first binding moietyincludes a linker that is or includes a site-specific recombinationmotif. In particular embodiments, polynucleotide segments encoding twocomponents of a binding moiety protein are separated by a number ofnucleotides, each of which encodes an amino acid of a linker.Accordingly, the number of intervening nucleotides must be a multiple ofthree, each nucleotide part of a codon encoding an amino acid of thebinding moiety. Various known site-specific recombination motifs are notamenable to this bifunctional use. That is, they do not include areading frame that can be transcribed or translated. In some instances,this may be because all reading frames include at least one stop codonor because the motif does not normally include a number of nucleotidesthat is a multiple of three. The present example describes theoptimization of site-specific recombination motifs in order to identifybifunctional variants thereof.

Libraries of variant attP and/or attB sequences may be produced byrandom mutagenesis starting from known, functional site-specificrecombination sites. The libraries may be cloned into test vectors. Inparticular, a set of vectors including attP variants may be produced anda set of vectors including attB variants may be produced. Optionally,these sites could be flanked with hydrophilic flexible amino acids(e.g., (Gly₄Ser)_(N)) of various lengths. It is noted that 9 of the 12reading frames cumulatively present in the attB and attP sites are openreading frames.

An assay has been designed that allows the identification of two vectorsthat, when present in a single cell that includes a phiC31 integrase,are able to recombine. Each vector includes a site-specificrecombination site. In a first test vector, a portion of achloramphenicol resistance (Cam R) gene (a construct including apolynucleotide encoding a protein that, when expressed, results inchloramphenicol resistance) is 5′ of and adjacent to a variantrecombination motif, here a variant or known attP motif. In a secondtest vector, the remainder of the CamR gene is 3′ of and adjacent to apotentially complementary recombination motif, here a variant or knownattB motif. Thus, the assay may be carried out using variants of an attPmotif on the first test vector and a known attB motif on second testvector, a known attP motif on the first test vector and variants of anattB motif on second test vector, or variants in both vectors.Recombination between a first test vector and a second test vector in acell including a phiC31 integrase results in the manifestation of a CamRphenotype.

In one particular example, the CamR gene includes an E. coli promoterand a CamR protein encoding region that includes an ATG proteininitiation site. The portion 5′ of the attP motif includes the promoterand ATG protein initiation site (FIG. 6, pATTP). The portion 3′ of theattB motif includes the remainder of the CamR gene (FIG. 6, pATTB). Thenucleotides of the attP motif are illustrated as underlined letters(FIG. 6, pATTP) and the nucleotides of the attB motif are illustrated aslower case letters (FIG. 6, pATTB). As shown in FIG. 6, recombinationbetween two such test vectors results in a product that includes an attRhybrid motif within a functional CamR gene (FIG. 6, pATTR). If the attRis not capable of expression such that each nucleotide of the attRcontributes to a codon that contributes an amino acid to the proteinproduct of the CamR gene, a CamR phenotype is not manifested.Accordingly, growth on LB media including Cam may be used to identifycells having a recombinant product with an attR that can be translated.Recombinant products present in these cells may be cloned, sequenced, orotherwise identified by any of a variety of means known in the art.

Utility of identified pairs of motifs may be tested. Pools of motifs maybe subcloned into a phagemid in the linker position of a polynucleotideencoding an scFv identified as being capable of binding a target protein(e.g., the MS2 coat protein). Phage may be produced from theVL-(subclone)-VH scFv vectors. These phage may be biopanned against anantigen using standard phage display methodology or another method ofbiopanning known in the art. Clones expressing functional scFv bindingmoieties may be isolated and the sequence of the linker may be amplifiedby PCR with subsequent confirmation by DNA sequencing or other methodsknown in the art. Clones may be retested to eliminate false positives.Clones may also be tested in HEK-293 cells.

While the example describes in particular the optimization ofbifunctional attP and attB motifs, it may be of value to furtheroptimize other motifs for use in conjunction with or instead of attP andattB. Accordingly, the methodology of the present example may be used tooptimize bifunctional variants of other site-specific recombinationmotifs. These may include FLP/FRT site-specific recombination motifs andother alternative recombinases such as those shown in Table I.

TABLE 1 Examples of site-specific recombinases Amino Works in Phage/acid Overlap SEQ mammalian name Host length region ID NO: cells?Tyrosine λ Escherichia 356 TTTATAC  7 yes integrases coli HK022Escherichia 357 AGGTGAA  8 yes coli P22 Salmonella 387 TTCGTAA  9unknown typhimurium HP1 Haemophilus 337 TTTTAAA 10 unknown influenzae L5Mycobacterium 371 CTTCCAA 11 unknown smegmatis Other Cre Escherichia 343ATGTATGC 12 yes tyrosine (P1) coli recombinases FLP Saccharomyces 423TCTAGAAA 13 yes cerevisiae XerC Escherichia 298 TGTACA 14 unknown coliSerine phiC31 Streptomyces 613 TTG 15 yes Integrases lividans R4Streptomyces 469 GAAGCAGTGGTA 16 yes parvulus TP901 Lactococcus 485TCAAT 17 yes lactis Other serine γō Escherichia 183 TATTATAAAT 18 yesrecombinases coli Tn3 Klebsiella 185 TATTATAAAT 19 unknown pneumoniaegin Escherichia 193 GA 20 unknown (phage Mu) coli

Example 6: Further Optimization of Bifunctional Site-SpecificRecombination Motifs

It may be beneficial, in some instances, to include in a bifunctionallinker more codons than would be necessary to encode only a bifunctionalrecombination motif. For instance, it may be beneficial to develop alonger linker or the addition may improve the efficiency oftranscription, translation, or recombination. The present exampleincludes the identification of additional sequence material of inclusionin a bifunctional linker that does not disrupt the recombinationfunction of the linker. For instance, vectors as described in theprevious example could further include additional nucleotide positions5′ or 3′ of the site-specific recombination motif. These additionalsequences could be one or more flexible hydrophobic cassettes, such as(Gly₄Ser)_(N). Such cassettes are commonly used as scFv linkersequences. These and other known linker sequences may be candidates forinclusion in bifunctional linkers in addition to a recombination motif.Selected bifunctional recombination motifs may be optimized by thesemeans in order to further increase efficiency of expression, bindingmoiety activity, or the like. In some instances, a polynucleotideencoding a bifunctional linker, or a portion thereof, may be flanked bymammalian splice sites, such that the portion of the bifunctional linkerencoded by the region flanked by the mammalian splice sites is onlyexpressed in non-mammalian cells.

Another mechanism for the optimization of bifunctional linkers may be toinsert restriction sites within the linker such that when a transcriptis generated that includes the linker, restriction enzymes remove aportion of the transcript, the removal resulting in the extension of theopen reading frame of the transcript. This technique may desirablyinvolve intracellular ligation of the cleaved ends of the transcriptsubsequent to restriction and prior to translation.

These techniques may be applied to optimization of one or morerecombinase enzymes or binding moieties. Efficiency may be by comparisonto standard laboratory constructs or wild type constructs.

Example 7: Optimization of Bifunctional LoxP Site-Specific RecombinationSites

A library of variant LoxP sequences may be produced by randommutagenesis starting from known, functional LoxP sites. M13 phagemidvectors may be produced such that each vector includes, 3′ of the GpIIIcassette, a first portion of a polynucleotide encoding LacZα, a known orvariant loxP, B. subtilis SacB, a second known or variant loxP element,and the remainder of the LacZα polynucleotide. SacB is lethal in E. coliwhen expressed in cells in the presence of sucrose. By contrast, loss ofSacB confers growth on sucrose-containing media. Accordingly, thevectors are transferred into TG1 E. coli cells including Cre recombinaseand incubated for a period sufficient to allow recombination. Thesecells are cultured on sucrose. Accordingly, only cells having excisedthe loxP-flanked SacB gene survive. Further, only cells in which thenewly formed hybrid loxP site, now positioned between the first andsecond portions of the LacZα gene, is bifunctional (i.e., eachnucleotide of the hybrid loxP site encodes an amino acid) will appearblue when cultured in the presence of X-gal. In various embodiments ofthis assay, the first loxP motif can be a variant loxP motif while thesecond loxP motif is a known loxP motif, the first loxP motif can be aknown loxP motif while the second loxP motif is a variant loxP motif,both loxP motifs can be distinct variant loxP motifs, or both loxPmotifs can be the same variant loxP motifs.

Example 8: Optimization of Various Aspects of the Techniques of thePresent Invention

Various aspects of the present invention may, if desired, be optimized.Optimization may occur be identifying from a plurality of variants thosethat are best capable of one or more particular functions.

One such function that may be optimized is the efficiency of secretionof the scFv into the periplasm. In various embodiments of the presentinvention, secretion of the scFv into the periplasm is directed by thepelB leader/signal peptide. In order to improve the efficiency ofsecretion of the scFv into the periplasm, pelB can be modified for usein conjunction with a mammalian splice acceptor site consensus sequence.Additionally, or alternatively, variation in the pelB sequence and begenerated and variants can be screened for improved secretion usingphage display. Alternative signal peptides (e.g., ompA, phoA) can besimilarly tested and/or modified as desired. In some instances, a signalpeptide may be used that operates in both bacterial and mammalian cells(e.g., an IL2 signal sequence).

A second function that may be optimized is the efficacy of SacB. If SacBdoes not effectively distinguish cells having been transformed with thefirst vector, and/or cells having been transformed with the first vectorbut having had the SacB cassette excised from the first vector, otherselectable markers may be employed. Other selectable markers such asgalK and thyA can be tested and/or modified as desired.

A third function that may be optimized is the expression of the chimericpolypeptide. In some instances, the chimeric polypeptide is an scFv-Fc.If an scFv-Fc is not well expressed, promoters other than the CMVpromoter can be tested and/or modified to improve expression. Otherregulatory sequences that may be tested include the hEF1-HTLV promoter,previously shown to support mammalian expression of scFv-Fc fusionbinding moieties, the EF1a promoter, or known IgG heavy chain and lightchain regulatory regions.

In addition, any binding moiety or framework of the present invention,including a chimeric polypeptide or any component before or afterrecombination of the first vector and the second vector, can beoptimized for codon usage in one or more particular cell types. Forinstance, some embodiments of the present invention include an scFvfirst binding moiety. In such instances, first binding moiety scFvs ofthe present invention may be optimized for codon usage in E. coli priorto the generation of a chimeric polypeptide. In any embodiment, codonusage can be changed, e.g., from a bacterial codon usage to a mammaliancodon usage.

It may be desirable to optimize the mammalian cell type for chimericpolypeptide expression. In some embodiments, the mammalian cell type isHEK-293. Optimization may involve assessment of chimeric polypeptideexpression in a variety of cell types. For instance, CHO cells may beused in place of HEK-293 cells.

In some instances, it may be that chimeric polypeptides of the presentinvention do not bind target antigen(s) with sufficient affinity forcertain applications. Techniques of affinity maturation are known in theart. Some may be performed in as little as one week. Other steps mayalso be taken. For instance, addition of the IgG dimerization domain isexpected to increase the affinity of a binding moiety for an antigen byfour to ten fold over scFvs due to avidity.

Efficiency of recombination may be optimized by modification of therecombinase gene. Various constitutive or inducible expression systemsmay be tested. For instance, the efficiency of inducible recombinaseenzymes, e.g., recombinase enzymes the expression of which can beinduced by the presence of arabinose, can be assayed. A wide variety ofpromoters, including, e.g., the tet promoter, are known in the art andcould be tested for optimization of recombinase expression to increaserecombination efficiency. Recombination efficiency can be monitored,e.g., by quantification of PCR amplification across an integration site.

Example 9: A Screen for Binding Moieties Targeting a Plurality ofAntigens with Subsequent Conversion

A library of vectors (e.g., a phage display library) encoding scFvbinding moieties for display is constructed. The library includesgreater than 10¹⁰ vectors, each encoding a variant scFv molecules andotherwise having essentially the same sequence as the other vectors inthe library. The vectors are constructed essentially according to thefirst vector of Example 1. Such a library has been generated by Kunkelmutagenesis. However, such libraries may also be generated by othermeans. The phage display scFv library may be screened for scFv bindingmoieties capable of binding various proteins (for example, about 10distinct proteins, e.g., USP11, SAR1A, CTBP2, PLAA, MAP2K5, CTBP1, CDK2,MAPK8, HSP90B1, and COPS5). The variant scFv molecules may, in someinstances, be screened in an automated screening pipeline, e.g., apipeline utilizing approximately one milligram of each antigen. scFvmolecules with the highest affinity and/or avidity for each antigen maybe selected by methods known in the art. scFv molecules selected in thismanner (e.g., the top 1-2 candidate scFv molecules) may be converted toIgG molecules, e.g., according to the methods described herein. In someinstances, a total of 10 to 20 scFv molecules may be selected forconversion to IgG molecules. Thus, this example describes the conversionof 10 to 20 scFv binding moieties.

Selected vectors may be transformed into HB2151 E. coli cells thatinclude a second vector constructed substantially according to Example 1and that further express Cre recombinase and phiC31 integrase. Thisresults in conversion of the scFv molecules to IgG molecules. HB2151 E.coli cells do not suppress amber stop codons.

Separately, the selected vectors may be transformed into HB2151 E. colicells that Cre recombinase but do not include a second vector of thepresent invention or a phiC31 integrase. These vectors undergo anexcision event resulting in the conversion of the scFv to an scFv-Fc.

The converted products may be transfected into and expressed in HEK-293cells. Binding moieties are purified from culture supernatants after 5-7days. The yield of the binding moieties (mg/L) and the affinity oravidity of the binding moieties for the relevant target antigen may bedetermined, for example, by Western blot and ELISA. As controls, theselected binding moieties may also be expressed in standard IgG and Fcfusion plasmids (e.g., pFuse-Fc, Invivogen) in HEK-293 cells. Inaddition, the selected scFv molecules may be expressed as solubleproteins in HB2151 E. coli cells.

Example 10: scFv to IgG Conversion Using the pAX688 Library VectorSystem

In one example, phagemid vectors, each encoding an scFv, are convertedby phiC31-mediated recombination into integrant vectors that may eachexpress, in mammalian cells, an IgG including the VL and VH regions ofthe scFv. This system utilizes intron splicing and integrase activity toperform subcloning. FIG. 7 shows the structure of the pAXM688 phagemidvector. In order from 5′ to 3′, the phagemid vector includes, e.g., amammalian promoter (P_(mam)), a mammalian signal peptide (Mam_(SP)), afirst 5′ mammalian splice site (Mam_(5′ss)), an E. coli promoter(P_(E.c.)), an E. coli signal peptide (Ec_(SP)), a first 3′ mammaliansplice site (Mam_(3′ss)), the VL gene, a second 5′ mammalian splice site(Mam_(5′ss)), an attP site-specific recombination motif, a second 3′mammalian splice site (Mam_(3′ss)), the VH gene, a third 5′ mammaliansplice site (Mam_(5′ss)), a suppressible stop codon (e.g., an amber stopcodon; TAG*), a gpIII gene, a non-suppressible stop codon (e.g., anochre stop codon; TAA*), a third 3′ mammalian splice site (Mam_(3′ss)),a CH gene, and a polyadenylation sequence (polyA). Due to the presenceof the amber and ochre stop codons located 5′ to and 3′ to the GpIIIgene, respectively, scFv fusion to gpIII can be controlled by ambersuppression. In other words, if this vector is present in an ambersuppressing strain of E. coli, an scFv-gpIII fusion is produced. If thisvector is instead present in a non-suppressing E. coli strain, then justthe scFv is produced.

The phagemid vector may, for example, be used to produce phage thatdisplay binding moiety proteins (e.g., scFv proteins including VH and VLdomains encoded by the VH and VL genes of the phagemid vector) on itssurface. Such phages may be used, for example, for phage display-basedbiopanning of the binding moiety proteins (e.g., to identify bindingmoieties, or antigen-determining regions thereof, capable of binding toa target molecule). A library of such phagemid vectors, each vectorexpressing a distinct scFv, can be generated according to methods wellknown in the art and/or methods as described herein.

As shown in FIG. 8, phiC31 integrase may be used to induce site-specificintegration of the phagemid vector to an acceptor vector (pAcceptor).From 5′ to 3′, the pAcceptor vector includes, e.g., an attBsite-specific recombination motif (not shown), a 5′ mammalian splicesite (Mam_(5′ss)), a mammalian signal peptide (Mam_(SP)), a mammalianpromoter (P_(mam)), a polyadenylation sequence (polyA), a polycistronicCamR complex (Ter RBS CamR), a CL gene, and a 3′ mammalian splice site(Mam_(3′ss)).

phiC31-mediated integration of the two vector yields an integrant vectorthat includes elements from both originating vectors. In this example,the integrant vector includes, from 5′ to 3′, e.g., a mammalian promoter(P_(mam)), a mammalian signal peptide (Mam_(SP)), a 5′ mammalian splicesite (Mam_(3′ss)), an E. coli promoter (P_(E.c.)), an E. coli signalpeptide (Ec_(SP)), a 3′ mammalian splice site (Mam_(3′ss)), the VL gene,a 5′ mammalian splice site (Mam_(5′ss)), an attL site-specificrecombination motif, a 3′ mammalian splice site (Mam_(5′ss)), a CL gene,a polycistronic CamR complex (Ter RBS CamR), a polyadenylation sequence(polyA), a mammalian promoter (P_(mam)), a mammalian signal peptide(Mam_(SP)), a 5′ mammalian splice site (Mam_(3′ss)), an attRsite-specific recombination motif, a 3′ mammalian splice site(Mam_(3′ss)), the VH gene, a 5′ mammalian splice site (Mam_(5′ss)), asuppressible stop codon (e.g., an amber stop codon; TAG*), a gpIII gene,a non-suppressible stop codon (e.g., an ochre stop codon; TAA*), a 3′mammalian splice site (Mam_(3′ss)), a CH gene, and a polyadenylationsequence (polyA).

The integrant vector can express a light chain gene (including the VLfused to the CL) and a separate heavy chain gene (including the VH fusedto the CH). As shown in FIG. 9A, the splice sites are located such thatthe bacterial regulatory elements and the attR site is spliced out ofthe light chain transcript, while the attL site and the gpIII gene isspliced out of the heavy chain transcript. The amber stop codon andochre stop codon is spliced out of the heavy chain transcript as well.In addition, integration results in activation of the CamR cassette,such that successful integrants can be selected for by growth on mediacontaining chloramphenicol. As shown in FIG. 9B, expression of the lightchain and heavy chain genes from the integrant vector produces pre-mRNAsin which bacterial and viral elements are located in introns. Thespliced, mature mRNA for the light chain includes the mammalian signalpeptide, VL domain, CL domain, and poly A tail. The spliced, mature mRNAfor the heavy chain includes the mammalian signal peptide, VH domain, CHdomain, and polyA tail. Thus, in mammalian cells, splicing may beutilized to eliminate undesired elements for mammalian expression,resulting in an expression vector ready to be transfected into mammaliancells (e.g., CHO cells) for IgG production.

In an alternate example, the pAX688 phagemid vector includes anorthogonal site-specific recombination site (e.g., an integration sitefor a recombinase other than phiC31), located between the gpIII andCH-encoding genes. In some instances, the orthogonal site-specificrecombination site is positioned upstream of a 3′ mammalian splice site.The counterpart of this orthogonal site-specific recombination site ispresent on a second acceptor vector, which may encode a functionaldomain such as those described herein. For example, the functionaldomain can be a ubiquitin ligase domain, knocksideways domain, or CARdomain. The CAR domain may, for example, include a CD3-zeta or CD28transmembrane domain, and/or a CD3-zeta, CD28, 41 BB, ICOS, FcεRIγ,influenza MP-1, VZV, and/or OX40 cytoplasmic domain, or any combinationor derivative thereof. In one instance, the acceptor vector includes apolynucleotide encoding, e.g., a CD3-zeta construct capable ofexpressing a CD3-zeta transmembrane domain and cytoplasmic domain (e.g.,14g2a-Zeta). Integration between the phagemid vector and the secondacceptor vector results in a second integrant vector capable ofexpressing a fusion protein including the scFv of the phagemid vector(or a derivative thereof including at least one, and preferably both, ofthe variable domains of the scFv of the phagemid vector) and theCD3-zeta domains, oriented with the CD3-zeta transmembrane domainpositioned between the scFv and the CD3-zeta endodomain. This can resultin a functional transmembrane receptor in which binding of the scFv to acognate antigen triggers a cytoplasmic zeta signal from the CD3-zetaendodomain. As such, if the second integrant vector is expressed in aT-cell, binding of the scFv to its cognate antigen results in activationof the T-cell. scFvs including antigen-determining regions capable ofrecognizing an antigen on a target cell type (e.g., malignant B-cells),can thus be integrated with CD3-zeta in this fashion and transfectedinto T-cells to produce T-cells to be tested rapidly, inexpensively, inmultiplex, and/or at high throughput. In one example, this scheme can beused to convert an scFv to an scFv-CD3-zeta fusion ready for T-celltesting in one day or less.

Example 11: Rapid scFv to IgG Conversion Using the pMINERVA VectorSystem

In one example, a phagemid vector (pMINERVA) encoding an scFv isconverted by phiC31-mediated recombination with an acceptor vector(pAcceptor) into an integrant vector that may express, in a mammaliancell, an IgG binding moiety including the VL and VH genes of the scFv(FIG. 10). This system utilizes intron splicing and integrase activityto perform subcloning. In some instances, the system operates in acompletely scarless fashion, e.g., in which all subcloning is performedby intron splicing and/or integrase activity, thereby obviating PCR,subcloning, and DNA sequencing steps. The phagemid vector includes from5′ to 3′, for example, a mammalian promoter (P_(mam)), a first 5′mammalian splice site (5′ss), a yeast promoter (P_(yeast)), B42transcription activation domain (B42), an E. coli promoter(P_(E. coli)), a first 3′ mammalian splice site (3′ss), a VH gene, asecond 5′ mammalian splice site (5′ss), a site-specific recombinationmotif (e.g., an attB or attP site; preferably an attP site), a second 3′mammalian splice site (3′ss), a VL gene, a third 5′ mammalian splicesite (5′ss), a suppressible stop codon (e.g., an amber stop codon), agpIII gene, a non-suppressible stop codon (e.g., an ochre stop codon), athird 3′ mammalian splice site (3′ss), and a CL gene. In this example,the pAcceptor vector includes, for example, a mammalian expressioncassette and, optionally, a bacterial expression cassette (e.g.,oriented antiparallel relative to the mammalian expression cassette).The mammalian expression cassette includes, from 5′ to 3′, a mammalianpromoter (P_(mam)), a first 5′ mammalian splice site (5′ss), asite-specific recombination motif (e.g., an attB or attP site;preferably an attB site), a first 3′ mammalian splice site (3′ss), a CHgene, a suppressible stop codon (e.g., an amber stop codon), and achloramphenicol resistance marker gene (Cam^(R)). In one example thebacterial expression cassette includes an E. coli promoter (P_(E. coli))and an Lpp-OmpA′ fusion. In some instances, the attB and attP motifs maybe swapped, such that the attB motif is present on the pAcceptor vector,and the attP motif is present on the phagemid vector.

phiC31 integrase may be used to induce site-specific integration of thephagemid vector and the pAcceptor vector. phiC31-mediated recombinationbetween these vectors produces the integrant vector, which includes allof the elements of the phagemid vector and the pAcceptor vector, exceptthat the attB and attP motifs are replaced by an attR motif and an attLmotif. As shown in FIG. 11A, the resultant integrant vector includes aheavy chain expression cassette and a light chain expression cassetteoriented parallel to each other. The physical linkage of the heavy andlight chains in the form of the integrant vector may be useful forimmunorepertoire screening. The heavy chain expression cassetteincludes, from 5′ to 3′, e.g., a mammalian promoter (P_(mam)), a 5′mammalian splice site (5′ss), a B42 transcription activation domain(B42), an E. coli promoter (P_(E. coli)), a 3′ mammalian splice site(3′ss), a VH gene, a 5′ mammalian splice site (5′ss), an attLsite-specific recombination motif, a 3′ mammalian splice site (3′ss), aCH gene, a suppressible stop codon (e.g., an amber stop codon), and achloramphenicol resistance marker gene (Cam^(R)). The light chainexpression cassette includes, from 5′ to 3′, e.g., a mammalian promoter(P_(mam)), a 5′ mammalian splice site (5′ss), an attR site-specificrecombination motif, a 3′ mammalian splice site (3′ss), a VL gene, a 5′mammalian splice site (5′ss), a suppressible stop codon (e.g., an amberstop codon), a gpIII gene, a non-suppressible stop codon (e.g., an ochrestop codon), a 3′ mammalian splice site (3′ss), and a CL gene. In oneexample, the antiparallel bacterial expression cassette for expressingthe Lpp-OmpA′ fusion from the pAcceptor vector is maintained. In someinstances, RNA editing may be used to alter splicing on the integrantvector (or other vectors, such as the phagemid vector or the acceptorvector), thus permitting rapid construction of bifunctional antibodies.

We have generated the components of the pMINERVA system and have testedthe phagemid vector and the integrant vector for their ability toproduce functional binding moieties in mammalian or bacterial cells(FIG. 11B). This included determining whether the various site-specificrecombination motifs can be used as linker regions connecting, forexample, two antigen-determining regions (e.g., VH and VL domains, or CLand VL domains). We showed that protein expression from pMINERVA vectorsystem could be detected in both HEK293 cells, which expressed IgGs, andin E. coli cells, which expressed scFvs. With respect to scFv expressionfrom the phagemid vector, we showed that the attP motif is suitable asan scFv linker region between the VH and VL domains, as indicated byscFv activity, but that the attB motif was not. As such, it may bedesirable to use the attP motif in the phagemid vector as the linkerbetween the VL and VH domains of the scFv. In some instances, either theattP or attB motif may be suitable for use as a linker in phage display,in which high expression of the protein incorporating the recombinationmotif as the linker may be less important. With respect to IgGexpression from the integrant vector, both the attR and attL motifs werefound to be suitable CL-VL linkers, with the resultant IgGs showingdetectable binding activity.

We also performed a feasibility analysis of whether the phiC31 integrasesite-specific recombination motifs can function as peptide linkers inscFvs or IgGs. The same scFv with three different linker sequences, WT(Gly4Ser)3, the phiC31 attB site, or the phiC31 attP site in readingframe 2, was produced. Each scFv was tested in an ELISA against thetarget protein or a non-relevant control. Anti-FLAG-HRP was used todetect a FLAG tag on the scFv and the ELISA was developed with Ultra TMBreagent. As can be seen in FIG. 12A, scFvs including the attP motif asthe VH-VL linker domain showed binding activity, but that scFvsincluding the attB motif did not. The same IgG with no linker between VLand CL (WT), or the recombined phiC31 integrase sites, attL or attR, inreading frame 2, was produced. Each IgG was tested in an ELISA againstthe target protein or a non-specific control. Anti-mouse-HRP was used todetect the IgGs and the ELISA was developed with Ultra TMB reagent. Asshown in FIG. 12B, IgGs including either an attL motif or an attR motifas the CL-VL linker (FIG. 12C) showed binding activity. All three IgGconstructs were expressed and functional. The attP motif also worked asa 12-amino acid linker between the CL and VL domains in functionalscFvs. These results confirm that the attP motif can function as apeptide linker in scFvs and IgGs, and that the attL and attR motifs caneach function as peptide linkers in IgGs. In further embodiments, suchrecombination motifs (e.g., attB, attP, attL, or attR motifs) may beuseful as CH-VH linkers on the heavy chain.

In an alternate example, the pMINERVA phagemid vector includes anorthogonal site-specific recombination site (e.g., an integration sitefor a recombinase other than phiC31), located between the gpIII and CLgenes. The counterpart of this orthogonal site-specific recombinationsite is present on a second acceptor vector, which is a CD3-zetaconstruct capable of expressing a CD3-zeta transmembrane domain andcytoplasmic domain (e.g., 14g2a-Zeta). Integration between the phagemidvector and the second acceptor vector results in a second integrantvector capable of expressing a fusion protein including the scFv of thephagemid vector (or a derivative thereof including at least one, andpreferably both, of the variable domains of the scFv of the phagemidvector) and the CD3-zeta domains, oriented with the CD3-zetatransmembrane domain positioned between the scFv and the CD3-zetaendodomain. This can result in a functional transmembrane receptor inwhich binding of the scFv to a cognate antigen triggers a cytoplasmiczeta signal from the CD3-zeta endodomain. As such, if the secondintegrant vector is expressed in a T-cell, binding of the scFv to itscognate antigen results in activation of the T-cell. scFvs includingantigen-determining regions capable of recognizing an antigen on atarget cell type (e.g., malignant B-cells), can thus be integrated withCD3-zeta in this fashion and transfected into T-cells to produce T-cellsto be tested rapidly, inexpensively, in multiplex, and/or at highthroughput. In one example, this scheme can be used to convert an scFvto an scFv-CD3-zeta fusion ready for T-cell testing in one day or less.

Example 12: Relative Positioning of Elements within Vectors

In some instances, the relative positioning of elements within a donorvector and an acceptor vector is important for dictating the positioningof elements within the integrant vector generated by recombination ofthe donor vector with the acceptor vector, For example, the placement ofthe E. coli promoter, attachment sites for phiC31 integrase, ribosomebinding site, and antibiotic resistance gene can be important for theproper selection of phiC-mediated recombination events with the pMINERVAvector system described herein.

FIG. 13 shows the sequence for a donor phagemid vector used to validatephiC31 function. In this donor vector, the attB site-specificrecombination site is located upstream of the ribosome binding site(RBS), spacer, and a chloramphenicol resistance gene (CAM). A portion ofan acceptor vector sequence used to validate phiC31 function is shown inFIG. 14. In this acceptor vector, the attP site-specific recombinationsite is positioned between a CAM promoter and a phiC31 gene. Notably,neither the donor vector nor the acceptor vector includes both the CAMpromoter and the CAM gene. As a result, a bacterial cell (e.g., an E.coli cell) containing either vector is sensitive to chloramphenicol.

Recombination between the donor vector and acceptor vector by arecombinase enzyme (e.g., phiC31) produces an integrant vector, of whicha portion is shown in FIG. 15. Due to the positioning of the CAMpromoter, RBS, spacer, and CAM gene relative to the correspondingsite-specific recombination sites in the donor and acceptor vectors, therecombined integrant vector includes, in order from 5′ to 3′, a CAMpromoter, an attR site-specific recombination site, a ribosome bindingsite, a spacer, and a CAM gene. As a result, a bacterial cell (e.g., anE. coli cell) containing the integrant vector (e.g., a cell in which thedonor vector and the acceptor vector had undergone phiC31-mediatedrecombination) expresses the CAM gene and is thus resistant tochloramphenicol.

Example 13: Splicing of a Synthetic Intron

In some instances, an intron (e.g., a synthetic intron) can be added toa vector of the invention (e.g., a first vector or a second vector),such that a polynucleotide positioned within the intron (e.g., apolynucleotide encoding a polypeptide or polypeptide fragment) isexpressed if the vector is in a prokaryotic cell (e.g., an bacterialcell, such as an E. coli cell), but not in a eukaryotic cell (e.g., amammalian cell or an insect cell) capable of mRNA splicing.

In one example, a synthetic intron containing the M13 gpIII fragment(e.g., as used for phage display) was introduced at the junction of theVH and CH region in the IgG expression vector (FIG. 16). The gpIIIintron sequence is as follows (SEQ ID NO: 21):

GTCGACCGTACGCA

AAGTCACCATCACCATCACCAT TAG ACTGTTGAAAGTTGTTTAGCAAAACCTCATACAGAAAATTCATTTACTAACGTCTGGAAAGACGACAAAACTTTAGATCGTTACGCTAACTATGAGGGCTGTCTGTGGAATGCTACAGGCGTTGTGGTTTGTACTGGTGACGAAACTCAGTGTTACGGTACATGGGTTCCTATTGGGCTTGCTATCCCTGAAAATGAGGGTGGTGGCTCTGAGGGTGGCGGTTCTGAGGGTGGCGGTTCTGAGGGTGGCGGTACTAAACCTCCTGAGTACGGTGATACACCTATTCCGGGCTATACTTATATCAACCCTCTCGACGGCACTTATCCGCCTGGTACTGAGCAAAACCCCGCTAATCCTAATCCTTCTCTTGAGGAGTCTCAGCCTCTTAATACTTTCATGTTTCAGAATAATAGGTTCCGAAATAGGCAGGGTGCATTAACTGTTTATACGGGCACTGTTACTCAAGGCACTGACCCCGTTAAAACTTATTACCAGTACACTCCTGTATCATCAAAAGCCATGTATGACGCTTACTGGAACGGTAAATTCAGAGACTGCGCTTTCCATTCTGGCTTTAATGAGGATCCATTCGTTTGTGAATATCAAGGCCAATCGTCTGACCTGCCTCAACCTCCTGTCAATGCTGGCGGCGGCTCTGGTGGTGGTTCTGGTGGCGGCTCTGAGGGTGGCGGCTCTGAGGGTGGCGGCTCTGAGGGTGGCGGTTCTGAGGGTGGCGGCTCTGAGGGTGGCGGTTCCGGTGGCGGCTCCGGTTCCGGTGATTTTGATTATGAAAAAATGGCAAACGCTAATAAGGGGGCTATGACCGAAAATGCCGATGAAAACGCGCTACAGTCTGACGCTAAAGGCAAACTTGATTCTGTCGCTACTGATTACGGTGCTGCTATCGATGGTTTCATTGGTGACGTTTCCGGCCTTGCTAATGGTAATGGTGCTACTGGTGATTTTGCTGGCTCTAATTCCCAAATGGCTCAAGTCGGTGACGGTGATAATTCACCTTTAATGAATAATTTCCGTCAATATTTACCTTCTTTGCCTCAGTCGGTTGAATGTCGCCCTTATGTCTTTGGCGCTGGTAAACCATATGAATTTTCTATTGATTGTGACAAAATAAACTTATTCCGTGGTGTCTTTGCGTTTCTTTTATATGTTGCCACCTTTATGTATGTATTTTCGACGTTTGCTAACATACTGCGTAATAAGGAGTCTTAATAACTAATCTCCTTCTCCTCCTCC C AGG GCCGTACGCTCGAGKey:

 His tag, amber stop codon, M13 gp3 gene fragment,  3 ′  splice site

HEK-293 cells were transiently transfected with the original wild-type(WT) vector or the variant containing the synthetic intron. Bothversions of the IgG vector were from a single-vector, dual-promotersystem. The modified WT IgG vector contained a truncated version ofgpIII within an intron located between the VH and CH regions. Withoutsplicing, there were multiple stop codons after the gpIII, which wouldresult in no production of the CH. With splicing, the CH would remainin-frame and would thus be expressed.

IgG was harvested from the culture supernatants and analyzed by SDS-PAGEanalysis under non-reducing (lanes 1 and 3) or reducing (lanes 2 and 4)conditions. The yield and purity of IgG was equivalent from the original(lanes 1 and 2) and intron-containing (lanes 3 and 4) constructs.

Example 14: Conversion of an scFv to Multiple IgGs and CARs Overnight

A vector system for antibody selection by phage display biopanning andin vivo conversion of the output pools of the selection to the chimericantigen receptor (CAR) or IgG format, using in vivo recombineering, isshown in FIG. 17. This scheme makes use of multiple serine integrasesthat recognize different site-specific recombination motifs toselectively recombine distinct portions of a phagemid vector encoding anscFv with a particular acceptor vector. This method may be useful, forexample, for rapid conversion to test Fc, enzyme fusions, CAR stalksequences, or any of the other elements of the phagemid vector and/orthe acceptor vector(s).

As shown in FIG. 17, phage containing a phagemid vector encoding an scFvare transduced into an E. coli strain expressing the BxB1 integrase andcontaining a lentiviral acceptor vector for creating the CAR fusion.BxB1-mediated recombination between the attP′ site on the phagemid andthe attB′ site on the lentiviral vector fuses the scFv to the hinge andtransmembrane and signaling domains of the TCR. In mammalian cells, anintron containing the M13 gp3 gene and attP site is removed by splicing.The recombination event also fuses an E. coli promoter to the zeocingene, allowing integrants to be selected on zeocin media (Zeo^(R)).Virus can be produced from the final vector in a mammalian packagingcell line and used, for example, to transduce Jurkat cells for CAR-Tassays.

Alternatively, the phage can be transduced into an E. coli strainexpressing the phiC31 integrase and containing an IgG acceptor vector.Recombination between the attP and attB sites (shown as attP* and attB*)fuses the VH to the CH and the mammalian promoter to the VL gene.Splicing in CHO cells eliminates an intron flanking the M13 gp3 gene andfuses the VL in frame with the CL. Integrants can be selected bychloramphenicol resistance (CAM^(R)). CHO cells can be transfected withthe final vector to produce full-length IgGs.

Example 15: Vector System for In Vivo Conversion of scFvs to ChimericAntigen Receptors (CARs) or IgGs

The present invention features methods for converting polypeptides of afirst type (e.g., scFvs) directly to polypeptides of a second type(e.g., IgGs and CARs) without requiring any sub-cloning and/or DNAsequence confirmation steps. In one example, a vector system is providedfor conversion (e.g., in vivo conversion) of an scFv to the chimericantigen receptor (CAR) format. This vector system may also be used toconvert the scFv to a full-length immunoglobulin G (IgG). The initialscFvs may be used, if desired, in antibody selection by phage displaybiopanning, and the output pools of the selection can subsequently beconverted to CARs or IgGs, e.g., as described herein. In some instances,the vector system makes use of bacteriophage integrases in E. coliand/or intron splicing in mammalian cells. Using this vector system, theoutput of phage selections can be screened directly on T-cells in theCAR format.

Vector System Incorporating Bacterial and Mammalian Control ElementsSuitable for phiC31-Mediated Conversion

A phagemid vector has been constructed that includes both bacterial andmammalian regulatory regions capable of supporting antibody expressionin bacterial and mammalian cells, respectively. The bacterial controlelements of the vector have been hidden within a mammalian intron (e.g.,as shown in FIG. 2). The vector includes a polynucleotide encoding anscFv fused to the bacteriophage M13 gp3 gene in bacteria. The scFv maybe converted to an IgG that can be expressed in mammalian cells bytransducing the phagemid into a second E. coli F⁺ strain. The phiC31serine integrase can be used to recombine the C_(H) gene from anacceptor plasmid to the V_(H) gene and to introduce controlling elementsupstream of the V_(L) gene. The attP recognition site for phiC31 can beused as a linker in the scFv. The vector is designed such that therecombined phiC31 integrase sites (attL or attR) between the variableand constant domains do not interfere with IgG expression or function(see, e.g., FIG. 10). For the purpose of generating the light-chainV_(L)-C_(L) fusion, mammalian splice sites flank the M13 gp3 gene,allowing the V_(L) to be fused to the C_(L) in mammalian cells. Thus,using this vector system, a single shuttle vector can be employed forphage library construction, phage display screening, and IgG antibodyproduction in mammalian cells.

Design and Testing of a Lentiviral Vector for Phage Display and CAR-T

(A) Creation of a Lentiviral Vector for CAR Expression.

In this example, we generated an acceptor plasmid for producing CARfusions based on a standard lentiviral vector. An scFv may be clonedinto this vector in-frame with a hinge (e.g., a CD8 hinge domain) and acytoplasmic domain (e.g., a transmembrane cytoplasmic signaling regionderived from TCRζ). In some instances, the scFv has an N-terminal FLAGtag to facilitate detection. Downstream of the TCR region and stopcodon, we may incorporate an internal ribosome entry site (IRES) and amarker, such as a gene encoding a fluorescent protein (e.g., an EGFPgene). The fluorescent protein may facilitate screening for transducedcells by immunofluorescence (IF) or fluorescence activated cell sorting(FACS). Virus may be produced in a packaging cell line and used totransduce cells (e.g., Jurkat cells). The percentage of EGFP+ FLAG+cells may be evaluated, for example, by FACS. To assess function, thetransduced Jurkat cells may be co-cultured with the antigen-expressingcells, and the expression of CD69 (an early marker of T cell activation)evaluated, e.g., by FACS.

(B) Incorporation of Both Mammalian and Bacterial Regulatory Sequences.

We have designed a regulatory cassette for both mammalian and bacterialexpression in which the bacterial control elements are hidden within amammalian intron (see, e.g., FIG. 2). To test its function in T cells,this regulatory cassette may be cloned in place of the CMV promoter inthe lentiviral vector for CAR expression. CAR expression in Jurkat cellstransduced with the virus may be evaluated and compared to expression inthe lentiviral CAR expression vector, e.g., as described in section (A)above.

(C) Testing of Mammalian Splice Sites Flanking Integrase Attachment Siteand M13 gp3 in Phage Display.

A synthetic intron flanked by natural splice donor and acceptorsequences may be generated, e.g., as described herein. The attachmentsite for a serine integrase may be encoded within this synthetic introndownstream of the gp3 gene on the phagemid (FIG. 18A). To test thesplicing, this synthetic intron may be cloned between the scFv and TCRζdomain of the CAR. As such, the intron containing the gp3 gene andintegrase attachment site may be spliced in mammalian cells. Propersplicing and expression of the CAR on the T-cells may be confirmed and,for example, compared to the constructs described in sections (A) and(B).

(D) Construction of Vectors for Testing Integrase-MediatedRecombination.

Serine integrases (e.g., a phage-encoded serine integrase) may mediatedirectionally regulated site-specific recombination between short attPand attB DNA sites without host factor requirements. Recombinationbetween the attachment site on a donor phagemid (attP) and thecorresponding attachment site on an acceptor plasmid (attB) in an E.coli strain expressing such an integrase (e.g., phiC31 integrase) mayresult in recombination of the scFv in the phagemid to the hinge (e.g.,CD8) and transmembrane cytoplasmic signaling region (e.g., derived fromTCRζ) on the lentiviral vector (see, e.g., FIG. 17). A strain for phiC31integrase expression in E. coli has been created and its functionalitydemonstrated (FIGS. 19A and 19B). Alternate integrases (e.g., BxB1) mayalso be used to enhance flexibility of the system. For example, thepromoter elements on the lentiviral vector may be replaced with an E.coli promoter such that recombination at the attachment site also fusesthe E. coli promoter on the lentiviral vector to an antibioticresistance marker (e.g., zeocin) on the phagemid (FIG. 18A), allowingselection for the integration event in E. coli. The efficiency ofrecombination may be determined by PCR screening colonies onnon-selective media.

(E) Validation of Vector Function.

In one example, a control anti-Tyro3 scFv was expressed from thephagemid vector described herein, and phage produced in E. coli. Asdescribed above, several exemplary anti-Tyro3 antibodies have beendeveloped by whole cell panning against Tyro3-expressing human cells.Phage and soluble scFv binding to cells expressing a desired targetmolecule (e.g., Tyro3), and not to a control cell line not expressingthe desired target molecule and/or expressing a different targetmolecule, may be confirmed, for example, by ELISA and/or FACS. E. colicontaining the lentiviral acceptor vector and expressing the alternateserine integrase (e.g., BxB1) may be transduced with the phage andintegrants may be selected by zeocin resistance. Virus may then beproduced from the recombined vector and used to transduce Jurkat cells.Functional display of the CAR fusion can be confirmed as describedherein.

Development of a Tri-Functional Vector System for Phage Display, IgGExpression, and CAR-T.

(A) Testing of attP linker on scFv. As described above, a vector hasbeen developed that utilizes an attachment site (attP) for the phiC31integrase as a linker in an scFv. Functional expression of the scFv hasbeen confirmed on phage and as soluble protein (FIG. 12A). It has alsobeen confirmed that the attP sequence between the V_(L) and C_(L)domains of the IgG did not affect IgG expression or function (FIG. 12B).The same linker may optionally be used in the CAR fusion. If desired,expression and function of a CAR containing the attP linker may beevaluated and compared to the CAR with the wild-type scFv linker (e.g.,as described herein).

(B) scFv Conversion to Both IgG and CAR.

The phagemid described above may be modified to incorporate, forexample, the human kappa light chain constant domain (C_(L)) downstreamof the intron containing the M13 gp3 gene, the alternate integrase(e.g., BxB1) attachment site, and the zeocin resistance gene (FIG. 18B).The scFv may also be modified to contain the attP linker sequencevalidated in step (A). Phage derived from this vector may be used totransduce an acceptor strain for IgG conversion (e.g., as shown in FIGS.10 and 17). In the acceptor strain, phiC31 integrase mediatesrecombination between the attP site on the phagemid and the attB site onthe acceptor vector to fuse the V_(H) on the phagemid to the human IgG1constant domain (C_(H)) on the acceptor vector and to fuse the CMVpromoter from the acceptor to the V_(L) gene on the phagemid. Theintegration event can be selected for in E. coli by expression of thechloramphenicol (CAM) resistance gene (FIG. 18B). DNA from CAM-resistantclones may be isolated and, e.g., used to transiently transfect CHOcells. Splicing in mammalian cells results in removal of the intron andfusion of the V_(L) to the C_(L) domain. Expression of the IgG can beconfirmed and compared to the expression level obtained with a standardvector. IgG function can be confirmed, for example, by ELISA and/or FACSagainst Tyro3-expressing cells. The IgG antibodies can be tested for theability to compete with the Gas6 ligand for Tyro3.

Other phage integrase attachment sites may be used as alternatives tophiC31. attP variant libraries may be generated, for example, by randommutagenesis. phiC31-functional integrase substrate sites can be selectedfor growth in, e.g., LB+ chloramphenicol media. Pools of theseintegrase-functional att sites can then be sub-cloned into the linkersite of a linker-less scFv between the V_(H) and V_(L) domains. Phagecan be produced from V_(L)-att*-V_(H) clones and biopanned against thetarget-expressing cells using, e.g., standard methodologies. Individualunique clones expressing functional scFvs and encoding functional attsequences can be re-tested. Those clones remaining positive can befurther tested in the IgG and CAR formats.

Production and Screening of a Human Combinatorial Antibody Library Usingthe Tri-Functional Vector

(A) Library Construction.

A functional phage display scFv library of, for example, at least 10¹⁰different members may be constructed, e.g., in a constant frameworkusing the vector system described herein. In some instances, such alibrary may be constructed by placing stop codons and restriction enzymecleavage sites in the complementarity determining regions (CDRs) of thechosen scFv framework, and then using Kunkel-based site directedmutagenesis to replace these stop codons with oligonucleotides encodingNNK codons.

(B) Phage Display Screen.

Stable cell lines have been generated that express cell surface targetsof relevance to cancer (e.g., Tyro3, NRP2, ErbB2, xCT, and AGTR1).Alternatively, cells expressing CD19, which is a validated target forCAR therapy, may be utilized. A screen by phage display using whole cellpanning may be performed to isolate de novo hits, for example, to Tyro3.The whole cell panning technology has been demonstrated to be usedsuccessfully to obtain binders to cell surface targets (e.g., Tyro3). Aspiked library containing the model anti-Tyro3 scFv used to develop thevector system may be included as a positive control.

(C) Production of scFv, IgG, and CAR-T Cells.

In one example, a set of clones (e.g., about 2, 3, 4, 5, 10, 20, 30, 40,50, 60, 70, 80, 90, 100, or more clones) from the selections arescreened by phage ELISA against the Tyro3 expressing cells and a controlcell line expressing a different cell surface receptor. The uniquebinders may be expressed as soluble protein from E. coli that cannotsuppress the amber stop codon between the scFv and M13 gp3 (e.g.,HB2151). The purified scFvs may be validated by ELISA againsttarget-expressing cells and control cells. Phage derived from thepositive hits may be used in parallel to transduce: (i) E. coliexpressing the BxB1 integrase and containing the lentiviral acceptorvector, and/or (ii) E. coli expressing phiC31 integrase and containingthe IgG acceptor vector. Lentiviral DNA may be extracted fromzeocin-resistant recombined clones of E. coli expressing the BxB1integrase and virus may be produced in the packaging cell line. Jurkatcells may then be transduced with the virus and the percentage of EGFP+FLAG+ cells can be evaluated, for example, by FACS. Plasmid DNA may beextracted from CAM-resistant recombined clones of E. coli expressingphiC31 integrase and, e.g., used to transfect CHO cells. Soluble IgGsmay then be purified from the culture supernatant and tested for bindingto the target cells by, for example, ELISA and/or FACS.

(D) Functional Validation of Selected Molecules.

The transduced Jurkat cells may be co-cultured with the targetexpressing cells. The expression of CD69 can be evaluated, for example,by FACS, as described herein. The IgGs may be tested for competitionwith the receptor ligand, if available.

Example 16: pMINERVA Transformer System with Orthologous Integrase Siteat the 5′ End, Linker Region, or 3′ End of the scFv

In some instances, the invention features a vector system (e.g., thepMINERVA phagemid vector shown in FIG. 20) for converting a firstpolypeptide (e.g., an scFv, F(ab′)2, Fab, Fab′ or Fv fragment, or animmunoglobulin, such as an IgG) to various chimeric polypeptides (e.g.,IgG, scFv, F(ab′)2, Fab, Fab′ Fv, CAR, or any other type of polypeptideas described herein), in which the recombination can occur at, forexample, any of the 5′ end, linker region, or 3′ end of a firstpolypeptide (e.g., scFv)-encoding polynucleotide within the vector. Forexample, recombination at the 5′ end of a first polypeptide may be usedto exchange promoters, controlling elements, and/or leader peptides.Recombination at the linker of a first polypeptide may be used to fuse aportion of the first polypeptide to a portion of a second polypeptide.For example, an scFv variable domain (e.g., a VH domain) may be fused toa constant domain (e.g., a CH domain), for conversion to an IgG.Recombination at the 3′ end of a first polypeptide may be used, forexample, to exchange a 3′ domain or to fuse the first polypeptide tovarious elements of interest. Such elements may include, for example,enzymes (e.g., β gal, alkaline phosphatase, and horseradish peroxidase),affinity tags (e.g., His6, FLAG, or proteinA), labels (e.g., GFP,Halotag, sfp, and SNAPtag), endosomal tags (e.g., ubiquitin ligase andFKB12), Avitags, sfp synthase, ACP-tag, TCRζ, and any other functionaldomains and/or binding moieties as described herein.

In one example, the pMINERVA vector includes an attP site positioned inthe linker region of the scFv (i.e., between the VH and VL domains), asshown in FIG. 20A. This attP site may, for example, be recombined with acognate attB site in an acceptor vector (e.g., pAcceptor) that includesa CH domain positioned such that the recombination results in formationof an integrant vector encoding the heavy chain and light chain of anIgG, which includes the VH and VL domains from the prior scFv of thepMINERVA vector. For example, the scFv Abs encoded on a pMINERVAphagemid donor vector as gp3-fusions may be screened in a phage displaybiopanning procedure to identify one or more phagemid clones encodingscFvs with certain desired biophysical properties (e.g., bindingspecificity and/or affinity for a target molecule). The identifiedphagemid clone may be transduced into an E. coli strain expressingphiC31 integrase and harboring, e.g., an IgG acceptor vector(pAcceptor). The recombination event may introduce a polyadenylationsignal site adjacent at the 3′ end of the CH gene. Furthermore, therecombination event may introduce a mammalian promoter and a functionalprotein initiation site 5′ to the VL gene. Of special note, the linkerbetween the VH and VL domains of the scFv is composed of a phiC31 36-bpattP site that is able to function as both: (i) a peptide linker betweenthe heavy and light variable domains, and (ii) a 36-bp functionalsubstrate for phiC31 integrase.

In a further example, the donor vector (e.g., pMINERVA) may be capableof integrating with multiple acceptor vectors (e.g., pAcceptor1,pAcceptor2, and pAcceptor3, as shown in FIG. 20B). In some instances,the donor vector may include a plurality of distinct orthologoussite-specific recombination motifs, each capable of recombining with aparticular cognate site-specific recombination motif. For example, thepMINERVA vector may include an attP# site 5′ relative to the scFv gene,an attP* site within the linker region of the scFv gene, and an attP′site 3′ relative to the scFv gene. Each of these recombination motifsmay be capable of recombining a particular cognate recombination motif(e.g., attB#, attB*, and attB′, respectively), which may be present onone or more distinct acceptor vectors. In certain instances, multipleorthologous cognate recombination motifs may be present on a singleacceptor vector. In other instances, each distinct acceptor vectorincludes one of the orthologous cognate recombination motifs.

For example, FIG. 20B shows three acceptor vectors, each including oneorthologous cognate recombination motif (shown as attB#, attB*, andattB′). pAcceptor1 includes an attB′ site downstream of a LacOP promoterand upstream of a polynucleotide encoding the components of a CAR (e.g.,a TCRζ domain and, optionally, a fluorescent marker protein, such asGFP). pAcceptor2 includes an attB* site positioned downstream of amammalian promoter (e.g., a CMV promoter) and upstream of a heavy chainconstant domain. pAcceptor3 includes an attB# site positioned downstreamof a yeast promoter. When the pMINERVA phagemid vector and one of theacceptor vectors is present in an E. coli host, an integrase protein(e.g., phiC31 integrase) may recombine the attP and attB sequences ofthe two vectors, thereby producing a polynucleotide encoding a singlechimeric molecule including both homing and donor vector sequences in apre-defined orientation. The system may be extended through the use oforthologous integrases. In one example, a second integrase, such asthose shown in Table 2 below, may be used to catalyze recombination atthe attP# site downstream of the VL region (pAcceptor1).

TABLE 2 Exemplary Integrases Protein Function in Phage name Host lengthmammalian host Tyrosine integrases Lambda E. coli 356 yes HK022 E. coli357 yes P22 S. typhimurium 387 unknown HP1 H. influenza 337 unknown L5M. smegmatis 337 unknown Other tyrosine recombinases Cre (P1) E. coli343 yes FLP S. cerevisiae 423 yes XerC E. coli 298 unknown Serineintegrases phiC31 S. lividens 613 yes R4 S. parvulis 469 yes TP901 L.lactis 485 yes Other serine integrases gamma-delta E. coli 183 yes Tn3K. pneumoniae 193 unknown gin E. coli 193 unknown

This recombination event could result in, for example, fusion of thescFv to a T-cell receptor to produce a CAR-T, and/or an exchange of theCL gene product downstream of the VL gene in a scFv or an IgG.Additional orthologous integrase sites (e.g., placed upstream of the VHgene, as in pAcceptor3) may be used to allow an exchange of promoters,leader peptides, or other elements of the donor and acceptor vectors.

Example 17: Spliced and Catenated Promoters

Vectors have been developed that are capable of expression in two ormore distinct cell types, with expression in each cell type controlledby distinct regulatory elements. For example, such a vector may includea bacterial promoter and a mammalian promoter, which control theexpression of a particular gene in bacteria or mammalian cells,respectively. At least two different strategies for such multi-promotervectors (e.g., vectors including dual expression promoters) can be used:(a) a spliced promoter (e.g., Pro^(splice), as shown in FIG. 21A) and(b) a catenated promoter (e.g., Pro^(cat), as shown in FIG. 21B).

In an example of promoter splicing, an scFv can be expressed in E. colifrom a lac promoter and in mammalian cells from a promoter (e.g., a CMVor EF1a promoter) using, e.g., a Pro^(splice) vector having the layoutshown in FIGS. 21A and 21C. In the Pro^(splice) vector, a mammalianpromoter (e.g., a CMV or EF1a promoter) controls the expression of amammalian signal peptide (e.g., a mammalian IgG heavy chain secretionsignal sequence) and a VH gene. The mammalian signal peptide of thePro^(splice) vector was designed to include an intron, which included aLacPO promoter/operator and a bacterial signal peptide. The bacterialsignal sequence overlapped with the splice acceptor site. Thus, in abacterial cell (e.g., E. coli), transcription from the bacterialpromoter within the mammalian intron may result in expression of thescFv in the bacterial periplasm. By contrast, in a mammalian cell (or inanother cell type capable of intron splicing), the bacterial regulatorysequences located in the intron may be removed by splicing, therebygenerating a fusion of the mammalian signal sequence to the VH gene. Theintron nucleotide sequence may include, in some instances, any promoterconsensus sequences, signal sequence consensus sequences, and splicesite consensus sequences known in the art.

In an example of the Pro^(cat) catenated promoter system, a mammalianpromoter (e.g., a CMV or EF1a promoter), polyhedron promoter (insectexpression), and LacPO promoter (bacterial expression) were placed, inorder, upstream of a ribosome binding site/Kozak fMet, polyfunctionalsignal peptide, and VH gene (FIG. 21B). In some instances, a catenatedpromoter may include at least a CMV promoter, LacPO promoter, signalpeptide (e.g., an IL2 signal sequence), and gene to be expressed, asshown in FIG. 21D. In the example of the Pro^(cat) system shown in FIG.21B, the ATG start sites were removed from the polyhedron and lacPOpromoters, such that the first ATG fMet start site for bacterial, insectand mammalian expression was identical. In this case, the same signalsequence was used for all three organisms. As a result, each of thethree catenated promoters drove expression of the signal peptide-VHfusion in the appropriate cell type. The vectors of the invention weretested, in one example, by determining whether a desired protein productwas generated by a cell type of interest. FIG. 22 shows the results oflight chain or IgG expression in mammalian cell culture. In one example,expression of a light chain gene incorporating a gp3 splice gene wascompared to that of a wild-type control light chain lacking the gp3splice gene (FIG. 22A). The two dual expression promoters, Pro^(splice)and Pro^(cat), were also tested for their ability to drive expression ofan IgG in HEK293 cells. An E1A promoter was used as a control. Both thePro^(splice) and Pro^(cat) vectors were shown to successfully driveexpression of the IgG at levels indistinguishable from that induced bythe control promoter (FIG. 22B).

Example 18: Antibody Library Design

The present invention provides methods and compositions useful forconverting a first polypeptide into a chimeric polypeptide. In someinstances, it may be desirable to convert a library of antibodies orantibody fragments into a library of chimeric polypeptides of adifferent type (e.g., a different type of antibody or antibody fragment,a CAR, a ubiquitin ligase, a knocksideways domain, or any otherpolypeptide type as described herein). For such antibody libraries, anyconstant and variable domains as known in the art may be used. In someinstances, the antibody or antibody fragment may be an immunoglobulin(e.g., an IgG, IgM, IgA, IgD, or IgE), scFv, F(ab′)2, Fab, Fab′ or Fv.In certain instances, the antibodies or antibody fragments of thelibrary may differ in the amino acid sequences of the variable domains,but not the constant domains. In particular instances, each of theantibodies or antibody fragments in a library may include the sameconstant framework. Exemplary constant frameworks that may be used insuch libraries are shown in FIG. 23.

Example 19: A Donor-Acceptor System for the In Vivo Recombineering ofscFv into IgG Molecules

Validation of recombinant antibodies selected by phage display oftenrequires early production of the cognate full-length immunoglobulin G(IgG). The conversion of phage library outputs to a full immunoglobulinvia standard subcloning can be time-consuming and/or limit the number ofclones that can be evaluated. Described herein is a vector system forconverting scFvs from a phage display vector directly into IgGs withoutany in vitro subcloning steps. This vector system, referred to herein aspMINERVA, makes use of site-specific bacteriophage integrases that areexpressed in E. coli and intron splicing that occurs within mammaliancells. In the pMINERVA system, a phage display vector contains bothbacterial and mammalian regulatory regions that support antibodyexpression in E. coli and mammalian cells. In one example, asingle-chain variable fragment (scFv) antibody is expressed on thesurface of bacteriophage M13 as a genetic fusion to the gpIII coatprotein. The scFv is desirably converted to an IgG that can be expressedin mammalian cells by transducing a second E. coli strain. In the secondE. coli strain, the phiC31 recombinase fuses the heavy chain constantdomain from an acceptor plasmid to the heavy chain variable domain andintroduces controlling elements upstream of the light chain variabledomain. In mammalian cells, splicing removes a synthetic introncontaining the M13 gpIII gene to produce the fusion of the light chainvariable domain to the constant domain. Phage displaying scFv andrecombinant IgGs generated using this system are expressed at wild-typelevels and retain normal function. Use of pMINERVA may thereforeeliminate the labor-intensive subcloning and DNA sequence confirmationsteps previously required to convert a scFv into a functional IgG Ab.

Summary

An exemplary low-cost system, pMINERVA, for the facile subcloning ofphage display scFvs into IgG molecules in vivo is described herein. Thesystem takes advantage of two genetic principles, recombination in E.coli and splicing in mammalian cells. As shown in FIG. 24A, the pMINERVAphage display vector contains both bacterial and mammalian regulatoryregions that support antibody expression in bacteria and mammaliansystems. The scFv is expressed as a fusion to the bacteriophage M13 gp3gene in bacteria and converted to an IgG that can be expressed inmammalian cells by transducing the phagemid into a second E. coli F⁺strain. In the second E. coli strain, the phiC31 serine integrase isused to fuse the heavy chain constant domain (C_(H)) from an acceptorplasmid to the heavy chain variable domain (V_(H)) and to introducecontrolling elements upstream of the light chain variable domain(V_(L)). Positive selection for the recombination events is built intothe system. To generate the light-chain V_(L)-C_(L) fusion, mammaliansplice sites flank the M13 gill gene, allowing the V_(L) to be fused tothe light chain constant domain (C_(L)) in mammalian cells. Thus, usingthe pMINERVA vector system, a single shuttle vector can be employed forphage library construction, phage display screening, and IgG antibodyproduction in mammalian cells.

Materials and Methods

Bacterial Strains and Vectors.

The TG1 E. coli strain (F′ (traD36 proAB+ laclq lacZΔM15) supE thi-1Δ(lac-proAB) Δ(mcrB-hsdSM)5, (rK-mK−) was purchased from Lucigen. Thetemplate phagemid, pAX1565, is a derivative of the phagemid, pAP-III6with a single-chain variable fragment antibody (scFv) fused to coatprotein III of bacteriophage M13. The scFv in pAX1565 is based on themonoclonal antibody, Herceptin (DrugBank #DB00072), and contains a(Gly₄Ser)₃ linker between the V_(H) and V_(L) domains.

Molecular Biology.

Standard cloning methods, as well understood in the art, were used forcloning, sub-cloning, DNA extraction, protein purification, protein andDNA quantitation. Required mutagenesis was done using site directedmutagenesis kits (Agilent). Synthetic genes were constructed at GeneArt(Life Technologies, Carlsbad, Calif.). Plasmid pCDF-1b was purchasedfrom Novagen (EMD Millipore, Billerica, Mass.). Restriction enzymes,ligases and polymerases were purchased from (New England Biolabs,Ipswich, Mass.) and used according to the manufacturer'srecommendations. Electro-competent cells were purchased from Lucigen(Middletown, Wis.). CHO Free style and HEK293 Free Style cells wereacquired from Life Technologies (Carlsbad, Calif.). Mammalian cellgrowth media was purchased from Life Technologies.

Construction of pDonor and pAcceptor Plasmids.

The phagemid pAPIII₆ was used as the template vector for the pDonorconstruct. The full-length M13 gpIII gene flanked by splice sites wassynthesized by GeneArt (Life Technologies, Carlsbad, Calif.) and clonedinto pAPIII₆ vector using Sal I and Xho I restriction sites. Theconstant region of the kappa light chain (C_(L)) and the SV40 late polyAsequence was synthesized by GeneArt and cloned into the above vectorusing the Xho I restriction site. Recombinants were sequence confirmedfor directionality. A synthetic scFv based on the anti-Her2 antibody,Herceptin, with the 36 bp attP sequence for phiC31 as a linker betweenthe variable heavy (V_(H)) and variable light (V_(L)) genes was clonedbetween the Hind III and Sal I sites in the vector. A Nu I site wasintroduced by site-directed mutagenesis (QuikChange, AgilentTechnologies, Santa Clara, Calif.) upstream of the phoA promoter in thevector. The synthetic promoters and leader peptides (e.g., Pro^(cat) orPro^(splice)) were cloned between the Nu I site and Hind III sites,replacing the phoA promoter upstream of the scFv gene. The origin andreferences (each of which is incorporated herein in its entirety) forall genes and regions included in the pDonor vector are listed in thetable shown in FIG. 251.

To engineer the pAcceptor vector, the phiC31 gene was synthesized byGeneArt (Life Technologies) and cloned into pCDF-1b (EMD Millipore,Billerica, Mass.) using Not I and Avr II restriction sites. The heavychain acceptor construct consisting of the human EF1a promoter, IL-2signal sequence, 36 bp attB sequence for phiC31 in frame with the signalsequence, human IgG1 constant domain, a ribosome binding site and spacerfollowed by the chloramphenicol gene (CAM), the BGH polyA sequence, andthe T7 transcription terminator, was synthesized by GeneArt (LifeTechnologies). This 3.3 Kb DNA region was cloned into the pCDF-1b/phiC31vector using the Acc65 I restriction site to generate pAcceptor.Recombinants were sequence confirmed. The origin and references for allgenes and regions included in the pAcceptor vector are listed in thetable shown in FIG. 251.

Construction of IgG Expression Test Vector.

A single vector system for IgG expression consisting of the EF1apromoter upstream of the light chain (variable light (V_(L)) andconstant light (C_(L)) regions) and a second mammalian promoter upstreamof the heavy chain (variable heavy (V_(H)) and constant heavy (C_(H))regions) was used to test individual components of the pMINERVA system.For the addition of the attL sequence between the signal sequence andV_(L), the attL duplex was cloned into the IgG expression vector usingthe Not I restriction enzyme (NEB) and sequenced to screen fordirectionality. For the addition of the attR sequence between V_(H) andC_(H), site-directed mutagenesis was performed to introduce the 36 basepair attR sequence following the manufacturer's protocol (QuikChange,Agilent Technologies). To introduce the M13 gpIII sequence flanked bysplice sites between V_(H) and C_(H) of the IgG expression test vector,the gene was synthesized by GeneArt (Life Technologies) and cloned intothe IgG expression test vector using BsiW I restriction sites.Recombinants were screened for directionality by sequencing. To exchangethe mammalian promoter driving the light chain of the IgG with Pro^(cat)or Pro^(splice), the promoter sequences were synthesized by GeneArt(Life Technologies) and cloned into the IgG expression test vector usingMlu I and Not I restriction sites. To exchange the mammalian promoterdriving the heavy chain of the IgG with Pro^(cat), the Pro^(cat)sequence was synthesized by GeneArt (Life Technologies) and cloned intothe IgG expression test vector using EcoR V and Nde I restriction sites.To exchange V_(H) and V_(L) regions in the IgG vector, the V_(H) genewas PCR amplified from a commercially available human IgG heavy chainexpression vector (Invivogen, San Diego, Calif.) and cloned into the IgGexpression test vector using Nde I and BsiW I restriction enzymes (NEB)and T4 DNA ligase (NEB). The entire light chain (V_(L) and C_(L)) and apiece of the SV40 late polyA sequence were PCR amplified from acommercially available human IgG light chain expression vector(Invivogen) and cloned into the IgG expression test vector containingthe correct V_(H) using Not I and Hpa I restriction sites. Recombinantswere sequence confirmed.

DNA Transformation.

In this example, transformation reactions were set up as follows: 0.5 μlligation product was mixed with 50 μl of TG1 electrocompetent cells(Lucigen) and added to a 0.1 cm gap cuvette. DNA was electroporated intobacterial cells using a Gene Pulser (Bio-Rad, at the following settings:1.6 kV, 200 ohms, 25 μF). One ml of recovery media was added and theelectroporated cells were transferred to 14 ml culture tubes and shakenat 37° C. After 1 hr, one hundred μl of each of the dilutions was platedonto LB plates containing ampicillin (100 μg/ml), and the plates wereincubated overnight at 37° C. Chemically competent NEB5α cells (NEB)were transformed according to the manufacturer's protocol. Briefly, 50μL of cells were incubated with 1 μL of DNA for 30 min on ice, heatshocked at 42° C. for 30 sec and 250 μL of recovery media was added.Cells were incubated while shaking for 1 hr at 37° C. and 100 μL wasplated on LB plates with 100 μg/mL of ampicillin.

Monoclonal Phage ELISA.

For vectors containing the Pro^(splice) promoter, a single colony oftransformed TG1 cells was picked off of a TYE/Amp/Glucose plate into a 2ml starter culture of 2YT supplemented with ampicillin (100 μg/ml) and1% glucose. Single colonies containing Pro^(cat) vectors were picked offof LB plates containing ampicillin (100 μg/ml) into a 2 ml starterculture of LB supplemented with ampicillin (100 μg/ml). Cultures wereincubated at 37° C. for 2-3 hours with shaking, diluted into 50 ml oftheir respective media, and further incubated at 37° C. with shakinguntil an absorbance at 600 nm of 0.4 was reached. Once the culturesreached mid-log phase, 10 ml were transferred into individual 15 mlconical tubes, and 5 μl of KM13 helper phage was added. After a 30 minincubation at 37° C. without shaking, tubes were centrifuged at 2000×gfor 10 minutes and the supernatants were aspirated. Pellets wereresuspended in 50 ml of appropriate media (Pro^(Splice): 2YTsupplemented with ampicillin (100 μg/ml), kanamycin (50 μg/ml) and 0.1%glucose; Pro^(cat): LB supplemented with ampicillin (100 μg/ml) andkanamycin (50 μg/ml)) and incubated at 30° C. with shaking overnight.After overnight incubation, the cultures were centrifuged at 15,000×gfor 10 minutes. Supernatants were transferred to an ELISA platepre-coated with the specific target antigen.

For coating of the ELISA plates, 100 μl/well of antigen diluted to 2.5μg/ml in 1×PBS was added to maxisorp ELISA plates (ThermoScientific,NUNC) and incubated overnight at 4° C. Wells were coated with eitherspecific antigen or with non-relevant protein to test for non-specificbinding. The wells were washed three times with PBS (250 μl/well) andblocked for 1 hr with 2% nonfat dry milk in PBS (MPBS). The wells werewashed for a total of three times with PBS. 100 μl of undilutedsupernatant containing phage was added to the ELISA plate and incubatedfor 1 hr at room temperature. Wells were washed three times with PBScontaining 0.01% Tween (PBS-T) followed by a 1 hr room temperatureincubation with anti-M13 monoclonal antibody conjugated to HorseradishPeroxidase (HRP; GE Healthcare, Piscataway, N.J.). The ELISA wasdeveloped by adding 100 μl TMB Ultra (Pierce, cat#34029) to each well,and the reactions were stopped with 50 μl 2M H₂SO₄. Plates were read at450 nm in a standard plate reader and fold over background (FOB) wascalculated by dividing the OD450 of a well containing phage on specificantigen by the signal of the same phage on non-relevant protein.

Production and Purification of Soluble IgG Antibodies.

IgG expression vectors were transiently transfected into mammalianHEK293 (Life Technologies; 293-F; cat#R790-07) suspension cells understerile conditions in a cell culture ventilation hood. On the day priorto transfection, the HEK293 suspension cells were diluted back to0.7×10⁶ cells/ml in 30 ml total volume using Freestyle 293 ExpressionMedium (Life Technologies). On the day of transfection, 24 μg of sterileIgG expression vector DNA was diluted in 3 ml Freestyle 293 ExpressionMedium and vortexed for 10 seconds. To the diluted DNA, 24 μl ofFectoPRO transfection reagent (Polyplus-transfection, New York, N.Y.)was added and vortexed for 10 sec. The DNA-transfection reagent mixturewas incubated at room temperature for 10 min. The DNA-transfectionreagent mixture was added to the 30 ml culture of HEK293 suspensioncells that were seeded the day prior. Post-transfection the HEK293 cellswere incubated at 37° C. in 8% CO₂ with shaking at 130 rpm for 72 hours,at which point 15 ml of fresh Freestyle 293 Expression Medium was added.The cultures continued incubating at 37° C. and 8% CO₂, shaking at 130rpm for an additional 48-72 hours. The transfected cells werecentrifuged at 1,000×g for 10 min and the IgG-containing supernatantswere transferred to new, sterile tubes. The IgG antibodies were purifiedfrom the clarified supernatants with 0.5 ml Protein A bead slurry. TheProtein A beads were washed three times with PBS and incubated with 45mL of IgG supernatant for one hour while rocking at 4° C. The Protein Abead+IgG mixture was poured into an empty 2 ml chromatography column andloaded via gravity flow. The columns were washed twice with 3 mL of PBSsupplemented with 1 mM PMSF and eluted with 1.5 mL of 0.1 M glycine atpH 3.0 and neutralized with 60 μl of 1 M Tris buffer at pH 9.0. Theeluate was analyzed by SDS-PAGE under reducing and non-reducingconditions. Final purified IgG was quantitated using the Coommassie Plusassay kit (ThermoFisher, cat#23236).

Human IgG ELISA on Protein.

For biotinylated antigens, ELISA plates were coated with 100 μL per wellof neutravidin at 10 μeμl/well) and blocked for 1 hr at room temperaturewith 3% bovine serum albumin (BSA) in PBS. The wells were incubated with1 μg/mL of biotinylated peptide (either specific target or non-relevantprotein) for 1 hr at room temperature after which they were washed threetimes with PBS (250 μL/well) and blocked again for 1 h with 3% BSA inPBS. After washing the wells with PBS 3×, the purified IgG antibodieswere added at 1 μg/ml in 3% BSA/PBS and incubated for 1 hr at roomtemperature. The wells were washed four times with PBS+0.01% Tween(PBS-T) and incubated with anti-human-IgG-HRP (ThermoFisher,cat#AH10404) diluted 1:5,000 in block for 1 hr at room temperature. Thewells were washed three times with PBS-T and the HRP-conjugatedsecondary antibody was detected with TMB reagent (100 μL/well) with a2-3 minute incubation. The reaction was stopped with 2M H₂SO₄ (50μL/well), absorbance was read at 450 nm and FOB was calculated bydividing the OD450 of a well containing IgG on specific antigen by thesignal of the same IgG on non-relevant protein.

Human IgG ELISA on Mammalian Cells.

HEK293 cells stably expressing a target antigen and HEK293 cells notexpressing the antigen were added to V-bottom ELISA plates (Phenix,cat#MPG-651101) at a concentration of 2.3×10⁶ cell/mL (0.15 mL perwell). Cells were blocked with 3% BSA for 30 min at room temperatureafter which they were centrifuged at 500×g for 4 min and the supernatantwas removed. Purified IgG was added to the cells at 1 μg/mL (100 μL perwell) and incubated while shaking for 1 hr at room temperature. Cellswere washed 2× with PBS, centrifuging the plate in between each wash at500× g for 4 min. Cells were incubated while shaking with anti-human-HRPat 1:5,000 in block for 1 hr at room temperature, Cells were washed 2×with PBS and transferred to a pre-blocked V-bottom plate and washed oncemore. 100 μL of luminescence reagent (Piece, cat #37069) was added tothe cells/well and transferred to a white bottom ELISA plate (NUNC,cat#436110). After a 2 min incubation the plates were read with aluminescence detector and FOB was calculated by dividing the relativeluminescence unit (RLU) of a well containing IgG on HEK293 cellsexpressing the target antigen by the RLU of the same IgG on HEK293 cellsnot expressing the target antigen.

Testing phiC31 Recombinase Function.

Competent TG1 cells containing the spectinomycin-resistant pAcceptorplasmid were prepared according to standard methods. The cells weretransformed with the pDonor or a mock-recombined control plasmidfollowing standard electroporation procedure (described above).Transformants were plated on LB media containing ampicillin (100 μg/ml)or chloramphenicol (10 μg/ml). The ratio of ampicillin tochloramphenicol-resistant transformants was determined.

Results

Cloning of phiC31 Phage Integrase and In Vivo Testing of FunctionalityUsing a Promotorless CamR Gene Polycistronic Message.

Phage-encoded serine integrases mediate directionally regulatedsite-specific recombination between short attP and attB DNA siteswithout host factor requirements. The phiC31 serine integrase can beused to induce recombination between two plasmids in E. coli. In thisexample, phiC31 is used to fuse the heavy chain variable domain (V_(H))on a phagemid vector (pDonor) to the heavy chain constant domain (C_(H))on a second plasmid (pAcceptor). These vectors are shown in FIG. 24A.For this approach to be feasible, the linker between the variable heavy(V_(H)) and variable light (V_(L)) domains of the scFv may contain a 36bp phiC31 integrase recognition site (attP or attB) that is able tofunction as both a peptide linker in the scFv and a functional substratefor phiC31 integrase.

The wild-type (Gly₄Ser)₃ linker between the V_(H) and V_(L) of a modelscFv (anti-Her2) in our phagemid vector was replaced with the phiC31integrase site (i.e., attP or attB). The phage-scFv were produced in E.coli and tested for function in a phage ELISA against the targetantigen, Her2, or a non-relevant control protein. As shown in FIGS.24B-24E, phage containing the attP linker bound selectively to Her2 withcomparable activity to phage containing the wild-type linker (FIG. 24B).Phage with the attB site as a linker in the scFv was unable to bind toits specific antigen.

Successful recombination between the attP site on the phagemid and theattB site on the acceptor plasmid generated a 36 base pair recombinedphiC31 site (attR) at the hinge junction of the variable heavy domainand constant heavy domain of the immunoglobulin (FIG. 24A). In addition,a 36 base pair recombined phiC31 site (attL) was produced between theleader peptide and variable domain of the light chain (V_(L)) (FIG.24C). Tested IgGs containing the attR or attL sequences at thesejunctions, respectively, expressed at wild-type levels and recognizedtheir respective target antigens (FIGS. 24D and 24E).

To test the function of phiC31 in our system, the gene was cloned into aplasmid (derived from pCDF-1b; Novagen) under the control of aconstitutive E. coli promoter (pCam; pACYC184) and transformed into theE. coli strain, TG1. A promoterless chloramphenicol resistance (camR)gene was placed 3′ of the phiC31 integrase attB site on the same plasmid(pAcceptor). Successful integration of the phagemid (pDonor) into thepAcceptor plasmid placed an E. coli promotor upstream of the pAcceptorcamR gene and produced a bicistronic gene-pair composed of theimmunoglobulin heavy chain and camR genes (FIG. 25A). The cells thatwere harboring this resulting co-integrated plasmid thereby becamechloramphenicol resistant. The phiC31-mediated integration efficiencywas tested in E. coli by transforming a pAcceptor TG1 strain with thepDonor plasmid and measuring the percent of ampicillin-resistanttransformants converting to camR. Conversion would only occur as aresult of successful co-integration. The ratio ofchloramphenicol-resistant (camR) transformants to ampicillin-resistant(ampR) transformants was compared with the ratio of camR to ampRtransformants using an already co-integrated plasmid in TG1 cells. Theresults demonstrated that the phiC31 integrase is able tosite-specifically recombine the pDonor vector into a pAcceptor vectorat >90% efficiency (FIG. 25B). No chloramphenicol-resistant colonieswere obtained when the pDonor lacked the attP site.

Design and Testing of Synthetic Intron Containing M13 gpIII.

While phiC31-mediated recombination was used to join the V_(H) to theC_(H) domain in the pMINERVA system, the light chain variable domain(V_(L)) domain in the scFv may also be fused to the light chain constantdomain (C_(L)) (FIG. 24A). In eukaryotic cells, large sequences can beefficiently removed from mRNA by the RNA splicing machinery. A syntheticintron was designed, which contained the M13 gpIII gene flanked byconsensus 5′ and 3′ splice site sequences. Thus, in E. coli, the scFv isexpressed on the surface of bacteriophage M13 as a genetic fusion to thegpIII gene, whereas in mammalian cells, the intron containing the gpIIIgene is excised, creating a fusion of the V_(L) to the C_(L) (FIG. 24A).In the absence of proper splicing, the C_(L) will be out of frame withthe V_(L), and functional IgG cannot be produced. As shown in FIG. 25C,introduction of splice sites between the scFv and gpIII gene did notinterfere with phage production or function. In HEK-293 cells, IgGexpression from the intron-containing vector was comparable toexpression from the original construct containing no intron, indicatingthat splicing was efficient (FIG. 25D; top panel). Both IgGs tested werefunctional and showed comparable activity in an ELISA against the targetantigen (FIG. 25D, bottom panel).

Design and Testing of Dual-Functional Promoters: Pro^(splice) andPro^(cat) Expression in Mammalian Cells and E. coli.

A dual-functional promoter that supports both E. coli and mammalianexpression was used to enable scFv production in bacteria and IgGproduction in mammalian cells. Two different promoter systems weretested: a promoter intron-splicing system (Pro^(splice)) and a catenatedpolyfunctional promoter system (Pro^(cat)) (FIGS. 25E-25H). In thePro^(splice) system, the EF1a promoter was followed by the mammalian IgGheavy chain secretion signal sequence that contains an intron. The lacpromoter/operator and bacterial signal peptide was contained within themammalian intron, and the bacterial signal sequence overlapped thesplice acceptor site. Thus, in E. coli, transcription from the bacteriallac promoter/operator within the mammalian intron resulted in expressionof the scFv in the bacterial periplasm, whereas in mammalian cells,splicing removed the bacterial regulatory sequences located in theintron, generating the mammalian signal sequence.

In the catenated promoter system (Pro^(cat)), the mammalian promoter isfollowed by a polyhedron promoter (for expression in insect cells) and abacterial promoter. The ATGs were removed from the downstream polyhedronand bacterial promoter such that the first ATG fMet start site forbacterial, insect and mammalian expression was identical. In this case,the same signal sequence was used for all three organisms. The Pro^(cat)developed here used the EF1a promoter for mammalian expression, the phoApromoter for E. coli expression, and the IL-2a signal peptide forsecretion in both systems. Phage displaying the model scFv was producedfrom both promoter systems at equivalent levels (FIG. 25G). In addition,the IgG yield from the dual promoter systems in HEK-293 cells wasequivalent to the yield using the EF1a promoter alone (FIGS. 25H-25J).

Thus, by combining together all of these elements, the pMINERVA systemcompletely eliminated the labor-intensive subcloning and DNA sequenceconfirmation steps currently required to convert a scFv into afunctional IgG antibody.

Discussion

Described in the present example is a vector system that enableshigh-throughput conversion of antibody fragments to full lengthimmunoglobulin G (IgG) molecules that can be directly validated instandard immunoassays. The screening platform described in this exampleis desirably used with single-chain variable fragments (scFvs), but canalso be used with any other polypeptide scaffolds known in the art,including, but not limited to, Fabs and yeast display libraries.

The pMINERVA system utilizes a phage integrase, phiC31, to inducesite-specific recombination between a donor and acceptor plasmid in E.coli to generate a fusion of the antibody heavy chain variable domain(V_(H)) to the heavy chain constant domain (C_(H)) and to introduceregulatory elements upstream of the variable light chain gene (V_(L)).Recombinases such as Cre and FLP may also be used for genomeengineering. As shown in the present example, however, phiC31 ispreferred because it is greater than 90% efficient at inducingrecombination between two plasmids in E. coli. Many additional knownserine- and tyrosine-integrases known in the art (e.g., BxB1 and lambda)can also mediate unidirectional, site-specific recombination and may besimilarly used in the present invention.

The phiC31 integrase has a 36 base pair (i.e., equivalent to 12 aminoacids) recognition sequence. The pMINERVA system utilizes incorporationof these integrase attachment sites in the linker of the scFv, andsubsequently, at the hinge junction between the heavy chain variable andconstant domains and between the signal sequence and light chainvariable domain. These 12 amino acid sequences did not interfere withphage production or IgG expression and function of the specificrecombinant antibodies, as shown herein. In some instances, attP or attBmutations that alter the resulting linker peptide to a more flexiblelinker sequence may be used to support efficient integration.Additionally, splice sites flanking the integrase attachment sites maybe incorporated into the vector to generate a seamless IgG. As shownherein, mammalian splicing can be used to excise the M13 gpIII gene andfuse the light chain variable domain (V_(L)) to the light chain constantdomain (C_(L)). Intron splicing has further been shown to enhance theexpression of recombinant proteins in mammalian cells.

Two dual expression promoter systems are described herein that wereeffective for E. coli and mammalian expression. One system utilizedmammalian splicing to excise bacterial expression elements, and thesecond system uses catenated promoters for mammalian, insect cell, andE. coli expression. The catenated promoter system required the samesignal peptide to work in both E. coli and mammalian cells. As shown inthe experiments described above, the IL-2 signal sequence was able tofunction as a secretion signal in bacteria. Other signal peptides thatwork in both mammalian and bacterial systems are known in the art andmay be alternately used for expression. The human EF1a promoter was usedto to build the dual function promoter systems described herein, butother promoters that enable high-level protein expression in mammaliancells (e.g., the CMV promoter) can be be used instead. The catenatedpromoter system further included the polyhedron promoter, such thatinsect cells could be used as an alternative to HEK-293 cells forhigh-throughput IgG production.

The current system was modeled on a human IgG1 antibody. However,additional pAcceptor plasmids can be constructed to extend the utilityof the system. Acceptor vectors containing other human immunoglobulinisoforms (e.g., IgG2, IgG3, IgG4, and IgM) can be generated, as well asacceptor vectors containing the constant domains for mouse or rabbitantibodies. Different types of 3′ fusions could also be generated,including, but not limited to, enzyme fusions, protein purificationtags, labels, and fusion-tags that can direct proteins to the endosome.Further, both acceptor and donor plasmids may be constructed forconversion to and/or from other chimeric proteins known in the art(e.g., antibody fragments and chimeric antigen receptors).

Example 20: Dual Expression Promoter Systems

The scFv to IgG reformatting methods described herein may utilize a dualexpression promoter system upstream of the affinity reagent. Two suchdual expression promoter systems have been successfully tested to date:a promoter intron-splicing system (Pro^(splice)) and a catenatedpolyfunctional promoter system (Pro^(cat)) (FIGS. 26A-26B). In bothsystems, the scFv is expressed in E. coli from a lacOPoperator/promoter. Expression in mammalian cell cultures has beensuccessfully tested from the Pro^(splice) and Pro^(cat) promoters usingeither the CMV or EF1A promoter (FIGS. 26C-26E). The splicing andco-integration did not significant affect expression in HEK293 cells orfunctionality.

Example 21: Development of Additional pAcceptor Plasmids

In this example, a set of pAcceptor plasmids was generated, e.g., foruse in the pMINERVA system (e.g., as described herein). The version ofthe pMINERVA system in this example utilizes the phiC31 integrase torecombine a donor phagemid with a unique acceptor plasmid in bacteria toefficiently create an IgG expression vector, pMINERVA (FIG. 27). Inmammalian cells, inherent cell splicing mechanisms may then remove thebacterial components of pMINERVA resulting in a functional IgG molecule.With a bifunctional, catenated promoter system (e.g., as describedherein), a scFv can be expressed in E. coli as a fusion to the M13 gpIIIcoat protein or as soluble protein prior to integration, and as a wholeIgG molecule in mammalian cells post-integration.

Experimental Design and Results

The pMINERVA system has a unique flexibility that allows for theconstruction of different 3′ fusions to extend the utility of thesystem. The types of fusions may include, for example, differentisotypes of IgG molecules, enzyme fusions, protein purification tags,CAR-Ts, and fusion-tags that can direct proteins to the endosomes. 3′fusion tags may be constructed, for example, using standard molecularbiological methods. Non-limiting examples of 3′ fusion constructs areshown in FIG. 28A. Testing of functionality may follow establishedprotocols for each of the tag types. In one example, a pAcceptor vectorencoding an scFv may be converted into a pMINERVA integrant vectorencoding an IgG (FIG. 28B).

Testing of Additional pAcceptor Vectors. NEB5alpha F′ strain E. colicells containing pAcceptors with one of the human IgG1 constant domain(hC_(H)) pAcceptor, rabbit constant domain (rC_(H)), or rabbit constantdomain with a C-terminal FLAG tag (rC_(H)-FLAG) were transduced withphage containing an anti-Her2 pDonor phagemid (with human V_(H), V_(L),and C_(L) kappa domains). The phiC31 integrase expressed from thepAcceptor catalyzed recombination between the attP site on the phagemidand the attB site on the pAcceptor plasmid. After a 3-hour recoveryperiod, the cells were plated on chloramphenicol-containing plates,which selected for co-integration. Plasmid DNA was extracted fromchloramphenicol-resistant colonies and analyzed on a 1% agarose gelstained with SYBR safe. The integrant vector was approximately 17kilobases in size. Proper co-integration of the vectors was confirmed(FIG. 29), with plasmids of the expected size generated. Vectors werealso sequenced to confirm proper integration.

To determine if the integrant vectors were capable of producing thedesired IgGs, HEK-293 Freestyle cells (Thermo Fisher) were transientlytransfected with the integrant vectors, and IgG was purified fromculture supernatants using Protein A resin. The purified antibodies wereanalyzed by SDS-PAGE under non-reducing (FIG. 30A) or reducing (FIG.30B) conditions. Both the fully human antibodies and the human-rabbithybrid chimeras were expressed.

The purified IgGs (at a concentration of 1 pg/ml) were analyzed by ELISAagainst titrating concentrations (0.01-1 pg/ml) of the target antigen,Her2 (FIG. 31). When protein A conjugated to HRP was used as thesecondary antibody for detection of the IgGs, the fully-human anti-Her2IgG1 antibody (H-H) showed comparable activity to the rabbit hybridchimeras (H-R and H-R-FLAG; FIG. 31A). In a second experiment,HRP-conjugated, anti-human polyclonal antibody was used as the secondaryantibody for detection of the IgGs. Since the variable domains and lightchain of the IgG were derived from human, the rabbit chimeric antibodiesshowed some cross-reactivity with the anti-human secondary (FIG. 31B).Lastly, when a HRP-conjugated, anti-rabbit polyclonal antibody was usedas the secondary antibody for detection, both rabbit chimeric antibodiesshowed good signal, and there was minimal cross-reactivity with thefully human IgGs (FIG. 31C).

The purified IgGs (at a concentration of 1 pg/ml) were also analyzed byELISA against titrating concentrations (0.01-1 μg/ml) of the targetantigen, Her2. A HRP-conjugated, anti-FLAG polyclonal antibody was usedas the secondary for detection of the IgGs. Only the human-rabbit hybridchimera with the C-terminal FLAG tag (H-R-FLAG) showed a signal in theELISA, as expected (FIG. 32).

pAcceptor Variants

In one example, a pAcceptor plasmid may be constructed for a pluralityof tag types (e.g., the first five tag types listed in FIG. 28A). It iscontemplated that pAcceptor plasmids may be constructed separately forthe Fc regions of, for example, mouse, rabbit, bovine, and the fiveprimary classes of human immunoglobulins (IgG, IgM, IgA, IgD and IgE).Differences in heavy chain polypeptides may allow these immunoglobulinsto function in different types of immune responses and at particularstages of the immune response. The polypeptide protein sequencesresponsible for these differences may generally be found in the Fcfragment. While there are five different types of heavy chains, thereare two main types of light chains: kappa (κ) and lambda (λ). Differentisotypes may display distinct structural and effector properties, suchas, e.g., complement-dependent cytotoxicity (CDC) and antibody-dependentcell-mediated cytotoxicity (ADCC). These properties may be key featuresin selecting the backbone to use for a particular therapeutic antibody.For example, in humans, there are four subclasses of IgG: IgG1, IgG2,IgG3 and IgG4 (numbered in order of decreasing concentration in serum).Variance among different subclasses is generally less than the varianceamong different classes.

Other Embodiments

All publications, patent applications, and patents mentioned in thisspecification are herein incorporated by reference.

While the invention has been described in connection with the specificembodiments, it will be understood that it is capable of furthermodifications. Therefore, this application is intended to cover anyvariations, uses, or adaptations of the invention that follow, ingeneral, the principles of the invention, including departures from thepresent disclosure that come within known or customary practice withinthe art.

What is claimed is:
 1. A method of converting a single-chain variablefragment (scFv) into a chimeric polypeptide, comprising: (a) providing afirst vector comprising, in order from 5′ to 3′, a first mammalianexpression control motif, a first E. coli expression control motif, asequence encoding a heavy chain variable region (VH) of the scFv, afirst site-specific recombination motif, a sequence encoding a lightchain variable region (VL) of the scFv, a 5′ mammalian splice site(Mam_(5′SS)), a fusion display protein sequence, a 3′ mammalian splicesite (Mam_(3′SS)), and a sequence encoding a light chain constant region(CL), and (b) providing a second vector comprising, in order from 5′ to3′, a second mammalian expression control motif, a second site-specificrecombination motif, and a sequence encoding a polypeptide; and (c)contacting the first vector and the second vector in the presence of arecombinase enzyme, wherein the recombinase enzyme combines the firstvector and the second vector in a site-specific manner to form anintegrant vector, and wherein the integrant vector expresses the VLfused to the CL and a separate VH fused to said polypeptide, therebyupon expression converting an scFv into a chimeric polypeptide.
 2. Themethod of claim 1, wherein said first vector is a phagemid vector. 3.The method of claim 1, wherein said second vector is a phagemid vector.4. The method of claim 1, wherein said first vector is a phagemid vectorand said second vector is not a phagemid vector.
 5. The method of claim1, wherein said first vector further comprises: (i) a second 5′mammalian splice site (Mam_(5′SS)) positioned between said firstmammalian expression control motif and said first E. coli expressioncontrol motif, and a second 3′ mammalian splice site (Mam_(3′SS))positioned between said first E. coli expression control motif and saidsequence encoding said VH of the scFv.
 6. The method of claim 5, whereinsaid first vector further comprises a leader sequence positioned betweensaid second 3′ mammalian splice site and said sequence encoding said VHof the scFv.
 7. The method of claim 1, wherein said first vector furthercomprises a leader sequence positioned between said first E. coliexpression control motif and said sequence encoding said VH of the scFv.8. The method of claim 1, wherein said first vector further comprises:an additional 5′ mammalian splice site (Mam_(5′SS)) positioned betweensaid sequence encoding said VH of the scFv and said first site-specificrecombination motif, and an additional 3′ mammalian splice site(Mam_(3′SS)) positioned between said first site-specific recombinationmotif and said sequence encoding said VL of the scFv.
 9. The method ofclaim 1, wherein said second vector further comprises: a further 5′mammalian splice site (Mam_(5′SS)) positioned between said secondmammalian expression control motif and said second site-specificrecombination motif, and a further 3′ mammalian splice site (Mam_(3′SS))positioned between said second site-specific recombination motif andsaid sequence encoding said polypeptide.
 10. The method of claim 1,wherein said polypeptide comprises a heavy chain constant region. 11.The method of claim 1, wherein said integrant vector expresses an IgGantibody.
 12. The method of claim 1, wherein said polypeptide comprisesa fusion protein.
 13. The method of claim 12, wherein said fusionprotein comprises a tag.
 14. The method of claim 13, wherein said tag isa FLAG, HA, Myc, V5, His, GST, MBP, AviTag, or streptavidin tag.
 15. Themethod of claim 12, wherein said fusion protein comprises a fluorescentprotein.
 16. The method of claim 1, wherein said providing step furthercomprises providing an additional vector comprising a polynucleotideencoding said recombinase enzyme.